Readme to markdown

[jlaehne]

• convert README file to markdown
• make badges work
• reorder to match Fix DOI and add more badges in README.md exspy#38
• Add link to website

Replaces #3350

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.54%. Comparing base (3b350ff) to head (6867e4f).

Additional details and impacted files

@@                  Coverage Diff                   @@
##           RELEASE_next_minor    #3351      +/-   ##
======================================================
- Coverage               80.55%   80.54%   -0.01%     
======================================================
  Files                     147      147              
  Lines                   21871    21871              
  Branches                 5144     5144              
======================================================
- Hits                    17618    17616       -2     
- Misses                   3036     3037       +1     
- Partials                 1217     1218       +1     

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[ericpre]

I ran twine check on the distribution file and it didn't complain!

Add a changelog entry?

[jlaehne]

Add a changelog entry?
done (I'm always not so sure whether we should include all minor maintenances in the changelog)

[ericpre]

In this case, I think the changelog is useful for developers, to be able to find the pull request easily, when it is fixing a typo or a dead link, adding a release note is not necessary.