Docserver: Add a note about config.rb to the docs README.

NOTRY=true

Review URL: https://codereview.chromium.org/291843004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@271852 0039d316-1c4b-4281-b951-d872f2087c98

chrome/common/extensions/docs/README

@@ -55,6 +55,8 @@ Editing docs
        and run compass from this (docs/) directory:
            compass compile .
        See http://compass-style.org/install to install compass.
+       See https://codereview.chromium.org/238303002/#msg6 for configuration
+       information (config.rb).
 
   2. Run 'server2/preview.py'