Update reference to TargetModuleScanner to use SigScanner service

[philpax]

The DI update replaced DalamudPluginInterface.TargetModuleScanner with a global SigScanner service. Need to update https://goatcorp.github.io/faq/development#q-how-do-i-hook-a-game-function to reflect that.

[snowoutwith]

I've had a go at this in my fork https://github.com/snowoutwith/faq but am unsure whether we want to keep the rest of the sample code as is or update it all to be DI style at once?