Added SnipMate to README

Hello - I added SnipMate to the README after seeing your note that it should be added in the Janus Google Group (https://groups.google.com/forum/?fromgroups#!searchin/janus-vimius/snipmate/janus-vimius/jZ9PBl8n2qA/9w8s0I9SxjsJ).  This is my first open source pull request, so let me know if I should be doing anything differently.  Thanks!