.pytool: Add MarkdownLintCheck plugin

This plugin runs markdownlint against all markdown files in a given
package to report linter errors.

See the following readme for me details:

  .pytool/Plugin/MarkdownLintCheck/Readme.md

Co-authored-by: Sean Brogan <sean.brogan@microsoft.com>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
3 files changed