Collaboration workflow

[toxypi]

1. Create a GitHub issue and describe a specific problem/idea. Assign the issue to yourself.

2. Create a corresponding branch:

git checkout main
git pull
git checkout -b ISSUE-<NUMBER>

3. Fix the problem in the new branch. Commit message must mention the issue number:

This closes issue #<NUMBER> on GitHub.

4. Create a pull request and choose the correct assignee:

git push --set-upstream origin ISSUE-<NUMBER>