build: add markdownlint tooling #972

Job	Run time
Add issues for new TODOs	11s
Testing / Chromatic	1m 50s
Publish / Publish	5m 12s
Build (macos-latest, 20) / Build (macos-latest, 20, false)	2m 58s
Build (ubuntu-latest, 20) / Build (ubuntu-latest, 20, false)	3m 19s
	13m 30s

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