docs: makes the README shinier ☀️

This is a slightly opinionated review since it:

• uses Unicode for emojis
• makes Proper nouns bold and Capitalize
• uses sh instead of bash for CLI commands
• adds an abbreviation (see https://kramdown.gettalong.org/syntax.html#abbreviations)

Otherwise fix some typos.

I would also suggest to add more emphasize (mostly with bold but sometimes with italic) on important words or notion in order to ease documentation reading. But I'm not the most qualified to know which are supposed to be most important so I'm leaving this to your discretion.