Update cheat_sheet.md (#1425)

Fixes #1262

This change fixes a few issues the cheat sheet had, and makes some additional improvements:

* Drop non-printable characters
* Use description text instead of formatting them as quotes
* Description before code (block/case titles/headlines) (like suggested in #1262, which I agree with)
* Use imperative mood (for the most part)
* Some wording improvements
* Some conciseness improvements (a cheat sheet should be concise, specific, and generalized at the same time)
* Consistently use `>` for commands and add missing returns (some code lines were missing, mixed, or wrong)