All markdown files are properly formatted now #181

This PR implements #162, and adds a precommit hook via lint-staged and husky. For the time being, I have only added an entry to lint-staged to format markdown (md) files. As well, all the md files have been formatted using the prettier settings that I copied from Storybook's settings.

Built everything locally and it looks good. I just did a smoke test navigating to some pages.

learnstorybook.com screeshot

Also, Skeletor approves of this PR.

Skeletor approves