Documentation Changes for Git Usage, Branching Model, and Release Management

[robertbartel]

Modifying and expanding documentation related to release management and new Git branching model.

Additions

• New RELEASE_MANAGEMENT.md doc with details on release process
• New GIT_USAGE.md doc with more technical details on Git usage and new branching model

Changes

• Updated CONTRIBUTING.md with more practical, day-to-day usage and initial setup Git information

Testing

1. None; doc updates only

Todos

• The specifics for "testing and quality pre-release tasks" during the release process need to be decided upon and documented.
• The exact process for peer reviewing changes made to release branches (e.g., bug fixes) during the release process needs to be decided upon and documented.

Checklist

• PR has an informative and human-readable title
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code follows project standards (link if applicable)
• Passes all existing automated tests
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future todos are captured in comments
• Visually tested in supported browsers and devices (see checklist below 👇)
• Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
• Reviewers requested with the Reviewers tool ➡️