docs: Document command to generate local html coverage report

[tpoliaw]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.04%. Comparing base (07c462c) to head (410c3ec).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1832   +/-   ##
=======================================
  Coverage   99.04%   99.04%           
=======================================
  Files         306      306           
  Lines       11589    11589           
=======================================
  Hits        11478    11478           
  Misses        111      111           

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[Villtord]

Not critically related to this change - do we have control over order of How-to pages? It feels like "checking coverage" should be close to "running tests" for me?

[tpoliaw]

It looks like it's alphabetical order with H1 sections promoted to full pages below their parent page (eg `Reusing an existing class follows Creating a new device because they're the same source file.

This is probably worthy of its own issue. The two example above probably shouldn't be listed as separate how-to guides.