[coreboot] coreboot code of conduct

[Marc Jones]

A coreboot code of conduct has been posted on the wiki.
  - http://www.coreboot.org/Code_of_Conduct

I have written a blog post about why we have a code of conduct.
  - http://blogs.coreboot.org/blog/2015/01/16/coreboot-code-of-conduct/

Feel free to give feedback on the policy and how else we can contribute to
a welcoming and collaborative environment.

Marc