document preferred mechanism to run the examples

[cdaringe]

problem

• it unclear as to the preferred mechanism on how to run the various included examples

discussion

perhaps steps such as:

• install per link-to-mutlicore-instructions
• run example via ocamlc ...

[kayceesrk]

I've updated the README https://github.com/ocaml-multicore/effects-examples#running-the-examples.