Add Code of Conduct

Fixes #1321

First try - content for Code of Conduct 
Do you want it more like this:

"Any organizer running a Yeoman hackathon, meet-up, conference, user group, or other type of event is encouraged to adopt and provide an appropriate Code of Conduct. Please refer to the Credits at bottom for further resources. Participants should also have easy access to contact information that will allow them to privately get help or report violations of the Code of Conduct." 

With these moved to the Credits section?

The [confcodeofconduct.com](http://confcodeofconduct.com) template is a good starting point. 

For more on adopting a code of conduct, see [Ashe Dryden's FAQ](http://ashedryden.com/blog/codes-of-conduct-101-faq_).