feat: add overview on generating bindings (#789)

Primarily adds the Generating Bindings section, but also updates the PDK
and SDK list to include more languages.

README.md

@@ -61,11 +61,11 @@ started:
 
 # Compile WebAssembly to run in Extism Hosts
 
-Extism Hosts (running the SDK) must execute WebAssembly code that has a [PDK, or Plug-in Development Kit](https://extism.org/docs/concepts/pdk), 
+Extism Hosts (running the SDK) must execute WebAssembly code that has a
-library compiled in to the `.wasm` binary. PDKs make it easy for plug-in /
+[PDK, or Plug-in Development Kit](https://extism.org/docs/concepts/pdk), library
-extension code authors to read input from the host and return data back, read
+compiled in to the `.wasm` binary. PDKs make it easy for plug-in / extension
-provided configuration, set/get variables, make outbound HTTP calls if allowed,
+code authors to read input from the host and return data back, read provided
-and more.
+configuration, set/get variables, make outbound HTTP calls if allowed, and more.
 
 Pick a PDK to import into your Wasm program, and refer to the documentation to
 get started:
@@ -74,13 +74,73 @@ get started:
 | ------------------ | ---------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------- | --------------------------------------------------------- |
 | Rust PDK           | <img alt="Rust PDK" src="https://extism.org/img/sdk-languages/rust.svg" width="50px"/>                     | https://github.com/extism/rust-pdk                            | [Crates.io](https://crates.io/crates/extism-pdk)          |
 | JS PDK             | <img alt="JS PDK" src="https://extism.org/img/sdk-languages/js.svg" width="50px"/>                         | https://github.com/extism/js-pdk                              | N/A                                                       |
+| Python PDK         | <img alt="Python PDK" src="https://extism.org/img/sdk-languages/python.svg" width="50px"/>                 | https://github.com/extism/python-pdk                          | N/A                                                       |
 | Go PDK             | <img alt="Go PDK" src="https://extism.org/img/sdk-languages/go.svg" width="50px"/>                         | https://github.com/extism/go-pdk                              | [Go mod](https://pkg.go.dev/github.com/extism/go-pdk)     |
 | Haskell PDK        | <img alt="Haskell PDK" src="https://extism.org/img/sdk-languages/haskell.svg" width="50px"/>               | https://github.com/extism/haskell-pdk                         | [Hackage](https://hackage.haskell.org/package/extism-pdk) |
 | AssemblyScript PDK | <img alt="AssemblyScript PDK" src="https://extism.org/img/sdk-languages/assemblyscript.svg" width="50px"/> | https://github.com/extism/assemblyscript-pdk                  | [NPM](https://www.npmjs.com/package/@extism/as-pdk)       |
-| .NET PDK           | <img alt=".NET PDK" src="https://extism.org/img/sdk-languages/dotnet.svg" width="50px"/>                   | https://github.com/extism/dotnet-pdk <br/>(supports C# & F#!) | https://www.nuget.org/packages/Extism.Pdk                 |
+| .NET PDK           | <img alt=".NET PDK" src="https://extism.org/img/sdk-languages/dotnet.svg" width="50px"/>                   | https://github.com/extism/dotnet-pdk <br/>(supports C# & F#!) | [Nuget](https://www.nuget.org/packages/Extism.Pdk)        |
 | C PDK              | <img alt="C PDK" src="https://extism.org/img/sdk-languages/c.svg" width="50px"/>                           | https://github.com/extism/c-pdk                               | N/A                                                       |
+| C++ PDK            | <img alt="C++ PDK" src="https://extism.org/img/sdk-languages/cpp.svg" width="50px"/>                       | https://github.com/extism/cpp-pdk                             | N/A                                                       |
 | Zig PDK            | <img alt="Zig PDK" src="https://extism.org/img/sdk-languages/zig.svg" width="50px"/>                       | https://github.com/extism/zig-pdk                             | N/A                                                       |
 
+# Generating Bindings
+
+It's often very useful to define a schema to describe the function signatures
+and types you want to use between Extism SDK and PDK languages.
+
+[XTP Bindgen](https://github.com/dylibso/xtp-bindgen) is an open source
+framework to generate PDK bindings for Extism plug-ins. It's used by the
+[XTP Platform](https://www.getxtp.com/), but can be used outside of the platform
+to define any Extism compatible plug-in system.
+
+## 1. Install the `xtp` CLI.
+
+See installation instructions
+[here](https://docs.xtp.dylibso.com/docs/cli#installation).
+
+## 2. Create a schema using our OpenAPI-inspired IDL:
+
+```yaml
+version: v1-draft
+exports: 
+  CountVowels:
+      input: 
+          type: string
+          contentType: text/plain; charset=utf-8
+      output:
+          $ref: "#/components/schemas/VowelReport"
+          contentType: application/json
+# components.schemas defined in example-schema.yaml...
+```
+
+> See an example in [example-schema.yaml](./example-schema.yaml), or a full
+> "kitchen sink" example on
+> [the docs page](https://docs.xtp.dylibso.com/docs/concepts/xtp-schema/).
+
+## 3. Generate bindings to use from your plugins:
+
+```
+xtp plugin init --schema-file ./example-schema.yaml
+  > 1. TypeScript                      
+    2. Go                              
+    3. Rust                            
+    4. Python                          
+    5. C#                              
+    6. Zig                             
+    7. C++                             
+    8. GitHub Template                 
+    9. Local Template
+```
+
+This will create an entire boilerplate plugin project for you to get started
+with. Implement the empty function(s), and run `xtp plugin build` to compile
+your plugin.
+
+> For more information about XTP Bindgen, see the
+> [dylibso/xtp-bindgen](https://github.com/dylibso/xtp-bindgen) repository and
+> the official
+> [XTP Schema documentation](https://docs.xtp.dylibso.com/docs/concepts/xtp-schema).
+
 # Support
 
 ## Discord

example-schema.yaml

@@ -0,0 +1,28 @@
+# yaml-language-server: $schema=https://xtp.dylibso.com/assets/wasm/schema.json
+# Learn more at https://docs.xtp.dylibso.com/docs/concepts/xtp-schema
+version: v1-draft
+exports: 
+  CountVowels:
+      input: 
+          type: string
+          contentType: text/plain; charset=utf-8
+      output:
+          $ref: "#/components/schemas/VowelReport"
+          contentType: application/json
+components:
+  schemas:
+    VowelReport:
+      description: The result of counting vowels on the Vowels input.
+      properties:
+        count:
+          type: integer
+          format: int32
+          description: The count of vowels for input string.
+        total:
+          type: integer
+          format: int32
+          description: The cumulative amount of vowels counted, if this keeps state across multiple function calls.
+          nullable: true
+        vowels:
+          type: string
+          description: The set of vowels used to get the count, e.g. "aAeEiIoOuU"