Merge pull request googleapis#752 from bshaffer/make-version-discrepancy-more-obvious

add banner to README to clarify version docs discrepancy

Author: bshaffer

README.md

@@ -2,6 +2,8 @@
 
 # Google APIs Client Library for PHP #
 
+> ### NOTE: If you arrived here from `developers.google.com`, you should be using the [v1-branch](https://github.com/google/google-api-php-client/tree/v1-master) of this repo
+
 ## Description ##
 The Google API Client Library enables you to work with Google APIs such as Google+, Drive, or YouTube on your server.