setup.md: use tabs for OS-specific instructions

[maxim-belkin]

I propose to update the setup page to use tabs for OS-specific instructions similarly to how they're used on workshop pages.
I also did the following changes:

• wrapped text to under 100 characters
• moved links to the end of the file
• fixed quotation marks around the word "Spotlight"

Snapshot

[gdevenyi]

Thanks for the formatting cleanup. I've always wondered if there's a nice text-reflowing formatter for markdown to do this more automatically...

[maxim-belkin]

Happy to help!