Document `notice` function

[technicalpickles]

trafficstars

In #hubot, @arnaudmm was trying to use thenotice method like:

robot.hear /^!toto$/, (msg) -> robot.adapter.notice "#systest2", "tototo"

This didn't work because the first argument is an envelope object that should have a user or room. This does work:

robot.hear /^!toto$/, (msg) -> robot.adapter.notice {room:"#systest2"}, "tototo"

[technicalpickles]

cc https://github.com/github/hubot/issues/1036 for more general conversation around supporting adapter-specific responses.