Fix auth example

README.md

@@ -61,10 +61,12 @@ oauth2_plugin = OAuth2Plugin(
     client_id='client_id', client_secret='client_secret', 
     token_url='https://example.com/oauth/token', audience='audience'
 )
+
 call_credentials = grpc.metadata_call_credentials(oauth2_plugin)
-channel = grpc.aio.insecure_channel('https://example.com/api/')
-request = GetRequest(user_id=1)
-stub = UsersStub(channel)
-stub.Get(request, credentials=call_credentials)
+
+with grpc.insecure_channel('localhost:50051') as channel:
+    request = GetRequest(user_id=1)
+    stub = UsersStub(channel)
+    stub.Get(request, credentials=call_credentials)
 ```