Document incompatibility with python 3.14

[tapastro]

This PR tries to document best install practices when a version of python exists that we have not yet tested against.

Tasks

• If you have a specific reviewer in mind, tag them.
• add a build milestone, i.e. Build 12.0 (use the latest build if not sure)
• Does this PR change user-facing code / API? (if not, label with no-changelog-entry-needed)
  • write news fragment(s) in changes/: echo "changed something" > changes/<PR#>.<changetype>.rst (see changelog readme for instructions)
  • update or add relevant tests
  • update relevant docstrings and / or docs/ page
  • start a regression test and include a link to the running job (click here for instructions)
    • Do truth files need to be updated ("okified")?
      • after the reviewer has approved these changes, run okify_regtests to update the truth files
• if a JIRA ticket exists, make sure it is resolved properly

[pllim]

Some comments. Thanks!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.41%. Comparing base (f1db9d7) to head (4ab15c6).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9865      +/-   ##
==========================================
+ Coverage   84.15%   85.41%   +1.25%     
==========================================
  Files         366      366              
  Lines       37800    37812      +12     
==========================================
+ Hits        31812    32297     +485     
+ Misses       5988     5515     -473     

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[pllim]

Thanks!