Outdated contributing instructions

[GoogleCodeExporter]

I believe the contributing instructions in the README are no longer accurate. 
They suggest that users follow Go's practice for contributing to snappy-go, 
citing the following link:

  http://golang.org/doc/contribute.html

But the contributing instructions for Go have changed since the switch to git. 
And, it's no longer clear to me how one would submit a patch to this repo for 
code review. Further, while Go now uses the Gerrit system for code review it 
looks like the older Rietveld system may still be in use here? But I just don't 
know for sure.

Original issue reported on code.google.com by bryan.matsuo on 23 Feb 2015 at 7:29