Polish up readme and fix a bunch of tpoyos

[Slackadays]

I polished the readme by applying the following changes:

• Format section headers in code blocks to add visual interest
• Replace checkmark and X symbols with the emoji versions to add visual interest, again
• Switch some wording from passive to active voice to make it easier to read, see https://developers.google.com/tech-writing/one/active-voice
• Compact/simplify some wording to made it easier to read, again
• Fix some nasti tpyoos

[jacob-carlborg]

Thanks.