Polish documentation

[janosg]

• Fix warnings in documentation build
• Update credits page to reflect recent contributions
• Update short descriptions where outdated
• Make sure contribution guidelines are up to date
• Link to scipy conference video
• Mention Stanford workshop with Ken and Michael

[codecov]

Codecov Report

Merging #384 (e265b05) into main (13c02f8) will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #384      +/-   ##
==========================================
- Coverage   92.64%   92.60%   -0.05%     
==========================================
  Files         207      207              
  Lines       16097    16097              
==========================================
- Hits        14913    14906       -7     
- Misses       1184     1191       +7     

Impacted Files	Coverage Δ
...magic/optimization/subsolvers/_trsbox_quadratic.py	84.89% <0.00%> (-2.86%)	⬇️
...ptimization/subsolvers/bounded_newton_quadratic.py	85.96% <0.00%> (ø)

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[timmens]

Approved, very nice PR. I only found two typos that should be fixed before the merge.