Clarify 'not an API' in docstring.

tseaver · tseaver · commit c6821d66880a · 2015-02-12T16:42:43.000-05:00
See: #622 (comment). [ci skip].
diff --git a/gcloud/_localstack.py b/gcloud/_localstack.py
@@ -13,7 +13,7 @@
 # limitations under the License.
 """Thread-local resource stack.
 
-Not an API.
+This module is not part of the public API surface of `gcloud`.
 """
 
 try:
