Add protocol overview (#7)

* Add diagram

* Added feedback

src/SUMMARY.md

@@ -1,8 +1,8 @@
 # Summary
 
 [Introduction](./intro.md)
-# [Protocol](./protocol/README.md)
-  - [Overview]()
+ [Protocol](./protocol/README.md)
+  - [Overview](./overview.md)
   - [Notarization](./protocol/notarization/README.md)
       - [TLS Handshake]()
         - [Key Exchange](./protocol/notarization/key_exchange.md)

src/overview.md

@@ -0,0 +1,6 @@
+# Overview
+
+The following diagram is a high-level protocol overview introducing the main components of
+TLSNotary.
+
+![TLSNotary Overview](tlsnotary_overview.png)

src/protocol/README.md

@@ -0,0 +1 @@
+# Protocol