Document what to do after an IRIS upgrade

[isc-pbarton]

Document what to do after an IRIS upgrade. Also includes some minor wording tweaks.
Resolves #648
Resolves #920

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 50.48%. Comparing base (f3a6db3) to head (27323a4).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #923      +/-   ##
==========================================
- Coverage   50.98%   50.48%   -0.50%     
==========================================
  Files          23       23              
  Lines        3109     3171      +62     
==========================================
+ Hits         1585     1601      +16     
- Misses       1524     1570      +46     

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