Clarify the structure of Bunch-Kaufman factors

[danielwe]

It took me a while to realize that the D in Bunch-Kaufman is block diagonal, not diagonal, so I thought I'd save others the trouble. I also mention P, U, and L for completeness, even though they are less surprising since they match the usual meaning of matrix factors with those names.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.77%. Comparing base (7f354f4) to head (260cbf2).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1341      +/-   ##
==========================================
+ Coverage   93.75%   93.77%   +0.02%     
==========================================
  Files          34       34              
  Lines       15778    15778              
==========================================
+ Hits        14792    14796       +4     
+ Misses        986      982       -4     

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[ViralBShah]

@danielwe - Invited you to have commit access.

[danielwe]

Was that meant for @araujoms in #1340? I don't see an invitation, and although I appreciate any recognition of my small contributions here and there, I'm not sure I should qualify for commit access

[ViralBShah]

I already sent it to @araujoms. And happy to have more help with triaging and small things. For now, I won't retrigger it though - but please let me know if you'd find it valuable.