[DNM] Update guesser docs

[lilyminium]

Relates to #4696

Do not merge -- I'll cherry-pick these commits into a real PR that's more easily reviewable after #3753 is merged. Just checking docs rendering for now.

PR Checklist

• [ ] Tests?
• [ ] Docs?
• [ ] CHANGELOG updated?
• [ ] Issue raised/referenced?

Developers certificate of origin

• [ ] I certify that this contribution is covered by the LGPLv2.1+ license as defined in our LICENSE and adheres to the Developer Certificate of Origin.

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📚 Documentation preview 📚: https://mdanalysis--4741.org.readthedocs.build/en/4741/

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 99.67949% with 1 line in your changes missing coverage. Please review.

Project coverage is 93.62%. Comparing base (48e9e01) to head (948d75b). Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
package/MDAnalysis/guesser/base.py	98.11%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #4741 +/- ## =========================================== + Coverage 93.60% 93.62% +0.02% =========================================== Files 173 187 +14 Lines 21464 22627 +1163 Branches 2993 3023 +30 =========================================== + Hits 20091 21185 +1094 - Misses 929 998 +69 Partials 444 444 ```

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[lilyminium]

Closing to cherry-pick commits into new PR once #3753 is merged.