Summary

This adds a CONTRIBUTINGmd file that will assist new people with coontributing to the library.

Checklist:

This PR has been tested
- The documentation has reflected the changes
- The code has been linted and formatted
This PR fixes an issue
This PR adds a new feature
This PR adds a breaking change
This PR is NOT a code change (e.g. documentation, README, ...)