Fix small mistakes in docs

[SkafteNicki]

What does this PR do?

Fixes #1962
Fixes many smaller mistakes in docs that does not render correct.

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?

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

Did you have fun?

Make sure you had fun coding 🙃

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📚 Documentation preview 📚: https://torchmetrics--1984.org.readthedocs.build/en/1984/

[codecov]

Codecov Report

Merging #1984 (04a4c5e) into master (4259943) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #1984   +/-   ##
======================================
  Coverage      86%     86%           
======================================
  Files         266     266           
  Lines       15185   15185           
======================================
  Hits        13131   13131           
  Misses       2054    2054           

[lantiga]

Great!