Explain namespace-level web application setting in documentation

[isc-pbarton]

Resolves #626

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.71%. Comparing base (90e07e5) to head (9767fb4).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #880   +/-   ##
=======================================
  Coverage   49.71%   49.71%           
=======================================
  Files          24       24           
  Lines        3305     3305           
=======================================
  Hits         1643     1643           
  Misses       1662     1662           

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