Adds usage examples to api-client samples and fixes copy/paste error in cloud-client/transcribe. [(#782)](GoogleCloudPlatform/python-docs-samples#782)

Author: gguuss

samples/snippets/README.rst

@@ -98,7 +98,7 @@ To run this sample:
     Google Cloud Speech API sample application using the REST API for batch
     processing.
     
-    Example usage: python translate.py resources/audio.raw
+    Example usage: python transcribe.py resources/audio.raw
     
     positional arguments:
       speech_file  Full path of audio file to be recognized

samples/snippets/transcribe.py

@@ -17,7 +17,7 @@
 """Google Cloud Speech API sample application using the REST API for batch
 processing.
 
-Example usage: python translate.py resources/audio.raw
+Example usage: python transcribe.py resources/audio.raw
 """
 
 # [START import_libraries]