Change from ruby mdl to node markdownlint, add
config file to root of project, delete old config
file, update exceptions, and fix one doc that
was didn't meet standards
If an MR only changes files within `doc/` we can save valueable CI time
by prepending a branch name with `docs-`. This danger rule helps educate
people about that fact.
On the other hand, if someone has a branch with a `docs` prefix or
suffix, the branch shouldn't contain any changes outside of the `docs`
directory
