gitflow-cjs 2.0

The primary purpose of this release is to clearly seperate gitflow-cjs and gitflow-avh by bumping the major version
to 2.

What's Changed

• Add better contributing section to README by @ChrisJStone in #1

New Contributors

• @ChrisJStone made their first contribution in #1

Full Changelog: 1.12.5...2.0.0