docs: revise readme

[inventarSarah]

A summary of the changes:

• correct typos and the likes
• content should be the same (nothing added, nothing removed) - some info has been consolidated or restructured, though
• add "alerts" to highlight information and make text more interesting
• add more subsections to help navigation
• renamed cli command "parameters", "options" to "flags" (like it says in the CLI's help message) -> let me know if you'd like to use another word
• add a "support and feedback" section