Improve CONTRIBUTING.md ?

[jgeewax]

PM2 seems to have a really nice guide to contributing. Maybe we can take some guidance from them?

https://github.com/Unitech/PM2/blob/master/CONTRIBUTING.md

[stephenplusplus]

It's kinda tricky, cause we have https://github.com/GoogleCloudPlatform/gcloud-common/tree/master/contributing for the generic "How to open an issue", but someone looking at our CONTRIBUTING.md file (as opposed to https://googlecloudplatform.github.io/gcloud-node/#/contributing won't see that).

Maybe we should just have a link back to the gcloud-common file at the top of ours?

[callmehiphop]

Should we move this to gcloud-common?

[jgeewax]

Yes, and yes.

[callmehiphop]

Closing per https://github.com/GoogleCloudPlatform/gcloud-common/issues/50