Fix blank lines in cheat sheets *again*

1. I should replace the variable name when I copy+paste a command around
2. Scratch all that fancy *[[:space:]]* syntax. It doesn’t work for me, and
I can’t find a mention of it in the bash manpage.
Allow comment lines in cheat sheet prompt section

A comment line is any line that starts with a '#' (no preceding
whitespace is allowed).
Update README.md

* add info about comments in prompts section
* update required commands (remove grep, add tput)
* use typographical quotation marks
Convert german typographic quotation marks to english ones

TIL they’re used differently; in german, like „this“ (‚this‘), in
english, like “this” (‘this’).
Use some more typographic quotation marks