Typos on Foundations cheat sheet, make use of example.com

Note about <variable> seemed a bit clunky reading-wise.

GitHub accounts are free, but clauses mentioning such are too close together. Leave "Setup" to describe what's needed, and keep the free part in the section that follows right after.

Torvalds was misspelt.

Prefer use of example.com since the other is real, parked.