Added basic nosurf wrapper and example

This is just a bare minimum example of using justinas/nosurf.

I think, we should at least add an optional `http.Handler` argument to pass to `SetFailureHandler()` but i'm not too sure how we should handle the whole `Exempt*()` thing. Maybe better add another example and/or documentation, that nosurf has to be setup by the dev if he needs full fledged excempt support.