Add markdownlint

[martincostello]

Add a Markdown linter.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.78%. Comparing base (056109e) to head (949d51a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2010   +/-   ##
=======================================
  Coverage   88.78%   88.78%           
=======================================
  Files          42       42           
  Lines         740      740           
  Branches       71       71           
=======================================
  Hits          657      657           
  Misses         38       38           
  Partials       45       45           

Flag	Coverage Δ
linux	88.78% <ø> (ø)
macos	88.78% <ø> (ø)
windows	88.78% <ø> (ø)

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