fix(docs): include v3.1 upgrade docs

[mubarak-j]

I noticed the v3.1 upgrade docs were missing from the website. I hope this fixes it.

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• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.21%. Comparing base (e0f4b00) to head (bf02e91).
⚠️ Report is 411 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #23529      +/-   ##
==========================================
- Coverage   60.27%   60.21%   -0.06%     
==========================================
  Files         345      345              
  Lines       59084    59084              
==========================================
- Hits        35610    35576      -34     
- Misses      20604    20631      +27     
- Partials     2870     2877       +7     

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