Merge pull request googleapis#2620 from daspecster/add-message-about-speech-not-published

Add message about API not being available yet.

Author: daspecster

docs/speech-usage.rst

@@ -5,6 +5,12 @@ The `Google Speech`_ API enables developers to convert audio to text.
 The API recognizes over 80 languages and variants, to support your global user
 base.
 
+.. warning::
+
+    This API, ``google-cloud-speech`` has not been released yet. In order to
+    test and explore this feature, you must install ``google-cloud`` from
+    source.
+
 .. warning::
 
     This is a Beta release of Google Speech API. This