Add a Contributing.md

[jwk6]

I happen to like what the Windows Terminal team does here - https://github.com/microsoft/terminal/blob/master/CONTRIBUTING.md#fork-clone-branch-and-create-your-pr

Fork, Clone, Branch and Create your PR
Once you've discussed your proposed feature/fix/etc. with a team member, and you've agreed an approach or a spec has been written and approved, it's time to start development:

1. Fork the repo if you haven't already
2. Clone your fork locally
3. Create & push a feature branch
4. Create a Draft Pull Request (PR)
5. Work on your changes

.. etc.

Also, answer the following question: How do I handle pulling down the code in the pull request to build and test locally, without actually completing the merge?

To fetch a remote PR into your local repo,

git fetch origin pull/ID/head:BRANCHNAME

where ID is the pull request id and BRANCHNAME is the name of the new branch that you want to create. Once you have created the branch, then simply

git checkout BRANCHNAME

Source: https://stackoverflow.com/questions/27567846/how-can-i-check-out-a-github-pull-request-with-git

[jwk6]

@NowinskiK I'll create a draft PR and finishing fleshing this out. I'll have a little time this weekend.