ISSUE-10 Add documentation

docs/FORWARDING.MD

@@ -0,0 +1,57 @@
+# Forwarding and Recording gRPC Communication
+
+The generated mock server is capable of forwarding an incoming request to another gRPC server, store the response and 
+return it to the caller. The recorded responses can be obtained by the `/recordings` endpoint in the REST server.
+
+## Limitations
+- Only insecure requests are supported.
+- If the same request is made more than once, only the latest response is recorded.
+- Error responses are not recorded at this moment.
+
+## Usage
+
+### Creating a forward
+To activate forwarding you must include the `forward` instead of the `response` field when creating the stub. Using the 
+provided `Greeter` service as an example, the stub would be created like this:
+
+`POST 127.0.0.1:1068/stubs`
+
+```json
+{
+    "fullMethod": "/carvalhorr.greeter.Greeter/Hello",
+    "request": {
+        "match": "exact",
+        "content": {
+            "name": "John"
+        }
+    },
+    "forward": {
+        "serverAddress": "yourserver:port",
+        "record": true
+    }
+}
+```
+
+You can control if the communication will be recorded through the `record` field. You must provide the remote server 
+address in the field `serverAddress`.
+
+When the mock server receive the request that matches the stub's request, it forwards the call to the external server, 
+record the request/response if recording is enabled, and return the response to the original caller.
+
+### Obtaining all recordings
+
+To obtain the recorded stubs, make a `GET` call to the `/recordings` endpoint.
+
+## Testing
+
+A sample server for the `Greeter` protobuf is available in `testing/example/server`. To testing the forwarding follow 
+these steps:
+
+- Generate the mock server for the provided `Greeter` and start it 
+- Start the server `testing/example/server`
+- Create a stub with forwarding enabled (see Usage)
+
+Now requests made to mock server will be forwarded to the real gRPC server and the communication will be recorded.
+
+Make a `GET` request to `recordings` to retrieve all the recorded communication.
+