Cheatsheet request: TypeScript

[hitesh-kumar123]

TypeScript isn't currently in the cheat sheet list, even though related languages like
JavaScript, ES6, and Dart are covered. It's one of the most widely used languages right
now (especially with React, Angular, Node, etc.), so I think it'd be a valuable addition.

I'd like to work on this myself and submit a PR. Just opening this issue first to flag
the gap / avoid duplicate work in case anyone else is already on it.

[hitesh-kumar123]

@Fechin can i work on this

[Quantodeluz]

You can work on it and put a pull request up for revision
Then Fechin can check the work and add it if it fits

Also do you plan on covering all of TS, or just the differences with JS?