Improve documentation on extending and changing .yo-rc.json

[vdininski]

I am trying to add requirejs using the .yo-rc.json file. However I am not entirely sure how it would work as I need to inject some stuff in more than one place in a single file (the requirejs main.js file). Another thing I noticed is that there are undocumented options - relativeToModule and undocumented template variables - filename.

[cgross]

Hmm. I don't think there's a solution to injecting twice in the same file currently. Sorry.