Add examples from Compose presentation to README

[hammer]

Having a quick example of how to use Oml from utop in the README would be nice. Bonus points for including your MNIST example as well.

[rleonid]

@hammer Would links to examples, maybe like a table of contents in the README suffice?

@smondet Do you think that oredoc would be a good fit here? I'd like to be able to easily transform the example scripts into documentation.

[smondet]

@rleonid oredoc can fransform ocaml code with special markdown comments into an HTML page with ocaml code-blocs:
https://github.com/hammerlab/ketrew/blob/master/src/test/Workflow_Examples.ml
http://seb.mondet.org/software/ketrew/Workflow_Examples.html
Happy to discuss adding features if that's not what you want :)