added compatibility notice

README.rdoc

@@ -1,5 +1,14 @@
 = google_docs_plugin
 
+
+== Compatibility
+
+
+The plugin is currently only compatible with redmine version < 2. I'm working on migrating it to redmine 2 in the
+branch `redmine-2`. Any help in this process would be greatly appreciated...
+
+
+
 == Overview
 
 
@@ -69,4 +78,4 @@ After this initial setup, you can edit the "Google Doc" field in issues and choo
 
 I'd wish to thank the following persons for contributing to this plugin :
 
-* Iacopo Spalletti
+* Iacopo Spalletti