Moving CONTRIBUTING out of docs to repository top-level.

[dhermes]

Also unifying the old docs/contributing.rst with the current contents of CONTRIBUTING.md.

[nathanielmanistaatgoogle]

"... and into repository" sounds like content is coming into source control from outside, which isn't the case. How about "Move CONTRIBUTING to repository top-level"?

[dhermes]

@nathanielmanistaatgoogle I also rewrote the original commit to say the same.

While doing it I realized that there is an existing CONTRIBUTING.md, which I added in #155!

I suggest we unify these two documents in a follow-up PR. WDYT?

[dhermes]

I should also mention that you can see the rendered RST on my branch: https://github.com/dhermes/oauth2client/blob/move-contrib/CONTRIBUTING.rst

[nathanielmanistaatgoogle]

Yes; it would be rude of us to maintain CONTRIBUTING.rst and CONTRIBUTING.md as separate documents.

[dhermes]

@nathanielmanistaatgoogle I went ahead and merged the two together. Can be seen at: https://github.com/dhermes/oauth2client/blob/move-contrib/CONTRIBUTING.md

[nathanielmanistaatgoogle]

LGTM!