add contribution guide that includes release process

[muvaf]

Description of your changes

Add a contribution guide with release process.

Fixes #64

I have:

• [x] Read and followed Upbound's contribution process.
• [x] Run make reviewable to ensure this PR is ready for review.
• [x] Added backport release-x.y labels to auto-backport this PR, as appropriate.

How has this code been tested

N/A

[jastang]

Fixes #64