doc: add notes about defining responses for the expected requests

Author: csernazs

doc/tutorial.rst

@@ -39,6 +39,12 @@ This tells that when the request arrives to the *http://localhost/foobar* URL,
 it must respond with the provided json. The library accepts here any python
 object which is json serializable. Here, a dict is provided.
 
+.. note::
+
+    It is important to specify what response to be sent back to the client
+    otherwise *pytest-httpserver* will error with ``Matching request handler
+    found but no response defined`` message on an incoming request.
+
 In the next line, an http request is sent with the *requests* library:
 
 .. code:: python

pytest_httpserver/httpserver.py

@@ -971,7 +971,15 @@ def expect_request(
         If `handler_type` is `HandlerType.ORDERED` an ordered request handler is created. Comparing to oneshot handler,
         ordered handler also determines the order of the requests to be served. For example if there are two ordered
         handlers registered, the first request must hit the first handler, and the second request must hit the second
-        one, and not vice versa. If one or more ordered handler defined, those must be exhausted first.
+        one, and not vice versa. If one or more ordered handler defined, those
+        must be exhausted first.
+
+        .. note::
+
+            Once this method is called, the response should also be specified by
+            calling one of the respond methods of the returned
+            :py:class:`RequestHandler` object, otherwise
+            :py:class:`NoHandlerError` will be raised on an incoming request.
 
 
         :param uri: URI of the request. This must be an absolute path starting with ``/``, a