Added Markdown Linter
Added Markdown Linter

Change Adds the pre-commit hook markdownlint which is
a ruby based linter for markdown. (https://github.com/markdownlint/markdownlint/blob/master/docs/configuration.md) The style guide can be found on https://github.com/markdownlint/markdownlint/blob/master/docs/RULES.md.

usgo/agagd,usgo/agagd,usgo/agagd,usgo/agagd