added info to docs: remember about coffee extension in require path

In node when you require('coffee-script') then when you require('path/to/file.coffee') then you can just write require('path/to/file') without extension, due to some changes in browserify v1 -> v1 you now need to add extension.

This is not natural if you're used to node way of things, so let's add this info till we work something out when it comes to default extensions.