Updated and improved documentation for contributing to AB

[marc-vdm]

Updated and improved file for contributing to AB

Checklist

• Keep pull requests small so they can be easily reviewed.
• Update the documentation, please follow the numpy style guide
• Categorize the PR by setting a good title and adding one of the labels:
  bug, feature, ui, change, documentation, breaking, ci
  as they show up in the changelog

[coveralls]

coverage: 50.184%. remained the same when pulling af1dd6a on marc-vdm:improved_contributing_file into 5a953a0 on LCA-ActivityBrowser:master.

[marc-vdm]

@bsteubing, the new guidelines can be seen as formatted MarkDown here: CONTRIBUTING.md.

Just let me know if you think changes need to be made or otherwise merge this PR :)

[marc-vdm]

@bsteubing Pinging you if you could please review CONTRIBUTING.md.

[bsteubing]

This looks very good - even the new version release instructions - well done!! :-)

[github-actions]

This issue has been implemented in the new release of Activity Browser 🚀 (version 2.9.3), you can get the new version by updating Activity Browser.

🤖beep boop! I'm a bot and this message was an automated action. If updating does not make sense for this issue, just ignore this.