updated documentation

README.rdoc

@@ -60,11 +60,12 @@ The second step is to connect your redmine account to your google docs account:
 6. This will open the google account page, which asks you to grant access to the redmine app.
 7. Click "Grant access"
 8. You will be redirected back to your redmint account page and should see a confirmation that your account has been connected
+9. Enable to custom field "google docs" in the admin area of redmine for the trackers which should use this field
 
 After this initial setup, you can edit the "Google Doc" field in issues and choose your documents via autocompletion.
 
 
-* Thanks
+== Thanks
 
 I'd wish to thank the following persons for contributing to this plugin :