Add contributing guide

[timothyubbens]

Description

This PR adds a CONTRIBUTING.md file. I'm new to Golang, so I've taken a first crack at the steps you'd like folks to follow to contribute to this repo, but I'm sure there will be a number of things that I've missed.

Fixes #7

Type of change

Documentation change

Checklist:

• [N/A] I have performed a self-review of my own code
• [N/A] I have commented my code, ensuring GoDoc readability and clarity in hard-to-understand areas
• I have made corresponding changes to documentation
• [N/A] I have added tests that ensure my fix is effective or that my feature works
• [N/A] Any dependent changes have been merged and published in downstream modules

If checklist items are unchecked please explain.

This change only includes a documentation update.

[madflojo]

👍

[madflojo]

Thanks Tim, this is great man!