docs: specify directives

[Borda]

What does this PR do?

improving reliability...
see options in https://www.sphinx-doc.org/en/master/usage/restructuredtext/directives.html

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

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📚 Documentation preview 📚: https://torchmetrics--2814.org.readthedocs.build/en/2814/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69%. Comparing base (d3894e1) to head (aa60766).
Report is 1 commits behind head on master.

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #2814   +/-   ##
======================================
  Coverage      69%     69%           
======================================
  Files         344     344           
  Lines       18828   18828           
======================================
  Hits        12975   12975           
  Misses       5853    5853