Gruber: How to correctly use a computer

John Gruber, referring to this new ad Apple released with their new iPad Pro: It's impossible to miss that MacBooks are just as much the butt of the jokes as any PC. "Do not touch the screen." "Your computer comes with a standard arrow cursor." "You must stay within reach of a Wi-Fi signal." "It does not have a camera; to connect one, refer to your instruction manual." And: I get it, all of these are things that make iPads fun and useful. The Mac can take it -- it's the mature workhorse plat...