Markdown

Add cheatsheet for Markdown (and it's variations)

REFERENCE

• https://github.com/wereturtle/ghostwriter/blob/master/resources/quickreferenceguide_en.md

[michaelpb]

great suggestion @Symbian9

It might make sense though to limit to one flavor since there are so many varieties. I'd probably say either CommonMark ( https://commonmark.org/ ) or GitHub Flavored Markdown ( https://github.github.com/gfm/ ) since they are the most popular and well-define

Any news?