Include badges in the documentation

[chrwm]

This repository could benefit from displaying badges to signal the standard of the code to other developers and improve the quality of the repository's documentation.

[Ludee]

I will move this issue to the organisation repo, since this should be done for all repos.

[Ludee]

I start with a collection of other repos that use a lot of badges for inspiration:

• https://github.com/oemof/oemof-solph
• https://github.com/PyPSA/PyPSA
• https://github.com/calliope-project/calliope

Here are some general pages for creating badges:

• https://betterprogramming.pub/add-badges-to-a-github-repository-716d2988dc6a
• https://shields.io/category/license
• https://dev.to/envoy_/150-badges-for-github-pnk
• https://badgen.net/
• https://github.com/dwyl/repo-badges