Update documentation with new location of example.clj
Rename :example -> :prod

Advanced compilation still fails to pass command line arguments…
Add externs file for node process module

process.argv was being optimized away in :advanced compilation mode.
[Frak](https://github.com/noprompt/frak) solves this by adding an
externs file for the node.js process module, so we'll do it to.

Note that that we will not include it in the exported JAR; the onus is
upon the library consumer to handle this sort of thing.