Propose new RFC for migrating off Sympa.

Heads up @nathenharvey 

I will post to the mailing list (hehe) and hopefully we can get some comments & have this reviewed by the next community meeting.
We tend to post to just the chef and chef dev lists with announcements, as well as always posting to the blog. We should resurrect opscode-announce in some form at least, as that likely has value.