Fix DOI badge and add more badges in README.md

[ericpre]

Progress of the PR

• Fix DOI in README.md,
• Add more badges in README.md,
• [n/a] docstring updated (if appropriate),
• [n/a] update user guide (if appropriate),
• [n/a] added tests,
• [n/a] add a changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• Check formatting of the changelog entry (and eventual user guide changes) in the docs/readthedocs.org:holospy build of this PR (link in github checks)
• ready for review.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.23%. Comparing base (f26aa4b) to head (114ccb1).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #34   +/-   ##
=======================================
  Coverage   87.23%   87.23%           
=======================================
  Files           7        7           
  Lines         329      329           
  Branches       73       73           
=======================================
  Hits          287      287           
  Misses         25       25           
  Partials       17       17           

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