Add github actions workflow

[napulen]

Add a Github Actions workflow for this repository (.github/workflows/...)

Using one of the peer-reviewed templates suggested by GH is preferred.

At the bare minimum, we want the following:

• [x] Basic linting with pylint, flake8 or similar
• [x] Run and verify pytest tests on commit/PR to main
• [x] Run on at least Python 3.8 and 3.9. The more the merrier.

[GabbyHalpin]

So the workflow has been created, and it builds python versions 3.6 and up. There may still be some tweaking to do on the file