Add a note for RVM users.
Add a note for RVM users.

atlrug/atlrug,atlrug/atlrug4,atlrug/atlrug4,jasnow/atlrug5,atlrug/atlrug,jasnow/atlrug5,jasnow/atlrug5,atlrug/atlrug4,atlrug/atlrug,jasnow/atlrug5-edge,jasnow/atlrug5-edge,jasnow/atlrug5-edge