Markdown linter

    USAGE:
        fx mdlint [flags]
    Flags:
     -enable value
           Enable a rule. Valid rules are 'bad-headers', 'bad-lists', 'casing-of-anchors', 'newline-before-fenced-code-block', 'no-extra-space-at-start-of-doc',
                       'no-extra-space-on-right', 'respect-col-length', 'respectful-code', 'simple-utf8-chars',
          'verify-internal-links'. To enable all rules, use the special 'all' name
     -filter-filenames string
           Regex to filter warnings by their filenames
     -json
           Enable JSON output
     -root-dir value
           (required) Path to root directory containing Markdown files

[mdlint source code](https://cs.opensource.google/fuchsia/fuchsia/+/main:tools/devshell/mdlint.fx)