ocaml-hap: rewrite README example to match the real API
The block had several broken pieces: corrupted tokens like
[Hap.turn_on_out\nlet session;], a positional [accessory_info]
argument to [pair_setup] (the real API uses [~ip] / [~port]), missing
[~fs] for [turn_on_outlet], and undeclared [eio*] mdx libraries.
Rewrite as a single [run ()] that goes through discover -> pair_setup
-> pair_verify -> turn_on_outlet against the actual signatures, and
add [eio] / [eio.core] / [eio.unix] to the mdx stanza.