Update the README with an example

Update the doc with an example and the supported liblxc API functions.
These should really be generated from the typespecs (and the liblxc
module should be generated from the typespecs too).

So far, the port works but crashes for some operations (like calling
stop/1 twice). Probably leaks memory like a sieve. Don't trust it.

Prototype quality: will probably re-write.