Custom GenTemplate docs: include Mac hotkeys for guillemets in XTend Editor

[tedepstein]

From John Heinnickel:

http://docs.reprezen.com/codegen_intro/#createGenTemplate comments about the keys for Guillemets not working on MacOS X. That's not exactly true-they're just different. Instead of Control< and Control->, you need to use Option-\ and Shift-Option-. As with Control-Space.

Auto-completion will often fill in the closing guillemet after just typing Option-, almost just like Control-Space, but with one important exception. Control-Space will only produce output if you are not already inside a pair of guillemets, but Option-\ will. Which means that you can create comment blocks readily with Option-\ by holding Option down through three taps of , but no such gesture is possible using just Control-Space.