docs: add an example with explicit compiler api to readme

README.md

@@ -42,7 +42,7 @@ To install Concrete Numpy from PyPi, run the following:
 You can find more detailed installation instructions in [installing.md](docs/user/basics/installing.md)
 
 
-## A simple example: numpy addition in FHE
+## A simple example
 
 ```python
 import concrete.numpy as cnp
@@ -62,6 +62,26 @@ for example in examples:
     print(f"Evaluation of {' + '.join(map(str, example))} homomorphically = {result}")
 ```
 
+if you have a function object that you cannot decorate, you can use the explicit compiler API instead
+
+```python
+import concrete.numpy as cnp
+
+def add(x, y):
+    return x + y
+
+compiler = cnp.Compiler(add, {"x": "encrypted", "y": "encrypted"})
+inputset = [(2, 3), (0, 0), (1, 6), (7, 7), (7, 1), (3, 2), (6, 1), (1, 7), (4, 5), (5, 4)]
+
+print(f"Compiling...")
+circuit = compiler.compile(inputset)
+
+examples = [(3, 4), (1, 2), (7, 7), (0, 0)]
+for example in examples:
+    result = circuit.encrypt_run_decrypt(*example)
+    print(f"Evaluation of {' + '.join(map(str, example))} homomorphically = {result}")
+```
+
 # For developers
 
 ### Project setup