Add docs for 'result_index' usage and a system test.

Author: daspecster

docs/speech-usage.rst

@@ -31,8 +31,8 @@ create an instance of :class:`~google.cloud.speech.client.Client`.
     >>> client = speech.Client()
 
 
-Asychronous Recognition
------------------------
+Asynchronous Recognition
+------------------------
 
 The :meth:`~google.cloud.speech.Client.async_recognize` sends audio data to the
 Speech API and initiates a Long Running Operation. Using this operation, you
@@ -169,6 +169,8 @@ speech data to possible text alternatives on the fly.
     ...                            encoding=speech.Encoding.LINEAR16,
     ...                            sample_rate=16000)
     ...     results = list(sample.streaming_recognize())
+    >>> print(results[0].result_index)
+    0
     >>> print(results[0].alternatives[0].transcript)
     'hello'
     >>> print(results[0].alternatives[0].confidence)

speech/tests/system.py

@@ -200,6 +200,7 @@ def test_stream_recognize(self):
 
         with open(AUDIO_FILE, 'rb') as file_obj:
             for results in self._make_streaming_request(file_obj):
+                self.assertIsInstance(results.result_index, int)
                 self._check_results(results.alternatives)
 
     def test_stream_recognize_interim_results(self):