Add markdown-toc recipe

- A brief summary of what the package does.

Generate a TOC at point for a markdown file.

- A direct link to the package repository.

https://github.com/ardumont/markdown-toc

- Your association with the package (e.g., are you the maintainer? have you contributed? do you just like the package a lot?).

I'm the maintainer.
I still love packages a lot.
(Cool that melpa deal with stable packages! Thanks!)

Cheers,