Add Git Versioning Docs

[brynnz22]

Issue #37

This PR includes the documentation for releases. I am guessing this will be a first go at it and we will do releases, see how we like it, adjust and iterate. I set the release cycle as every first business day of the month if there are changes to main. We can change this how we like. For now, the CHANGELOG.md is manual. There are potential tools we can use to automate this, but I'm not sure that level of automation is necessary given the nature of this repo. The release part of Github auto-generates a description of the release anyway based on the merged requests. Right now I just include an outline in the CHANGELOG. We will have to update/erase some of it with our first release.

All Submissions:

• [x] Have you followed the guidelines in our Contributing document?
• [x] Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• [x] Does your PR link to an issue?
• [x] Have you described the changes this PR will make?

New Notebook Submissions:

• [ ] Have you included a summary of the notebook in the README.md included updated links to the notebook?
• [ ] Does your PR include links to the new notebook (in the branch) for review using nbviewer, Colab, and reviewnb? These three are the preferred ways to review changes and additions to notebooks during review.

Notebook Fix Submissions:

• [ ] Does your PR include links to the updated notebook (in the branch) for review using nbviewer, Colab, and reviewnb? These three are the preferred ways to review changes and additions to notebooks during review.

[brynnz22]

From Bea: Maybe make release date two weeks after nmdc-schema release to apply any new schema changes and keep in sync with new schema changes.