Document diferences between other monokai implementations

[alerque]

There are a ton of other monokai implementations out there for vim already. For example I've been using this one which includes both gui and cterm modes plus airline support.

I would suggest adding a note to the README briefly outlining any design or implementation choices that set this implementation apart from the ones that have been floating around forever.

TL;DR: What makes this tastier?

[patstockwell]

Thanks for the feedback! 😄