Add Tutorial

[paf31]

No description provided.

[kozak]

Hi Paf, How would you like the tutorial to look - would something like this be ok? https://github.com/kozak/purescript-foreign-generic-example/blob/master/src/Main.purs

Actually this doesn't add much more than the examples in test. The only thing that wasn't clear was the JS structure for sum types { tag, contents : { } }. I'll try to add a test like this tomorrow.

[paf31]

@kozak An example project could be really useful, but I was thinking more along the lines of an extended README.