add contributing.md

Change-Id: Ia3284a90dfbbaaf655facd885a8ef13858bdb2c9
change double quotes to backticks for md awesomeness

Change-Id: Ife68c9c67d36ffec24927176ab519f7cb08976a8
moved CONTRIBUTING.md to top of repo; link to CONTRIBUTING.md in README.md

Change-Id: Ibe1def5c0c5e1e7f6eb0da344badc53d18f2ecb3
fix link to CONTRIBUTING.md in README.md

Change-Id: I53a24c061d0610a9c4b3c515c7d5ba7c04ae9f54
Merge changes I53a24c06,Ibe1def5c,Ife68c9c6,Ia3284a90

* changes:
  fix link to CONTRIBUTING.md in README.md
  moved CONTRIBUTING.md to top of repo; link to CONTRIBUTING.md in README.md
  change double quotes to backticks for md awesomeness
  add contributing.md