docs: use https for extra nav links

[orbeckst]

Fixes #

Changes made in this Pull Request:

• The docs sidebar had links using unencrypted http pointing to home page and userguide. Changed to use https.

PR Checklist

• Issue raised/referenced?
• Tests updated/added?
• Documentation updated/added?
• package/CHANGELOG file updated?
• Is your name in package/AUTHORS? (If it is not, add it!)

Developers Certificate of Origin

I certify that I can submit this code contribution as described in the Developer Certificate of Origin, under the MDAnalysis LICENSE.

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📚 Documentation preview 📚: https://mdanalysis--5093.org.readthedocs.build/en/5093/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.85%. Comparing base (96f0b67) to head (47aba19).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #5093   +/-   ##
========================================
  Coverage    93.85%   93.85%           
========================================
  Files          178      178           
  Lines        22122    22122           
  Branches      3129     3129           
========================================
  Hits         20763    20763           
  Misses         902      902           
  Partials       457      457           

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