added documentation for server-facing stubs (#186)

README.md

@@ -192,6 +192,36 @@ EchoStreamResponse(value='hello')
 EchoStreamResponse(value='hello')
 ```
 
+This project also produces server-facing stubs that can be used to implement a Python
+gRPC server.
+To use them, simply subclass the base class in the generated files and override the
+service methods:
+
+```python
+from echo import EchoBase
+from grpclib.server import Server
+from typing import AsyncIterator
+
+
+class EchoService(EchoBase):
+    async def echo(self, value: str, extra_times: int) -> "EchoResponse":
+        return value
+
+    async def echo_stream(
+        self, value: str, extra_times: int
+    ) -> AsyncIterator["EchoStreamResponse"]:
+        for _ in range(extra_times):
+            yield value
+
+
+async def start_server():
+    HOST = "127.0.0.1"
+    PORT = 1337
+    server = Server([EchoService()])
+    await server.start(HOST, PORT)
+    await server.serve_forever()
+```
+
 ### JSON
 
 Both serializing and parsing are supported to/from JSON and Python dictionaries using the following methods: