Add documentation on releasing new versions

[LunarEclipse363]

This should include:

• some file documenting the process (done in f548a88)
  • where to change the version number (pyproject.toml)
  • details on git tagging
  • info on github actions
• possibly automate Sphinx getting the version from pyproject.toml (the config is a Python script) (done in 9c2456a)
• add a github action for releases (see how the inventree fork does it) (done in 983dd8d)

Other notes:

• add a PR template that has a "notable changes have been added to the changelog" checkbox (see github docs)