Fix README.md

[GeoMinesGold]

I am aware that other pull requests asked for my first point, but not the rest, so I created this anyway:

• Update README.md to reflect hyprshot being in the standard Arch repositories instead of the AUR
• Remove the annoying $ and # to make copy-pasting easier
• Fix a typo
• Use sh in code blocks for simplicity instead of having multiple types (i.e., shell and bash)