bh-escort: document the alarm() and sleep() usage
bh-escort: document the alarm() and sleep() usage

According to `man 2 sleep` sleep may be implemented using SIGALRM. To
avoid conflicts we need to be careful to avoid calling sleep() after
calling alarm(); the code as-is does this, but to avoid future problems
document the limitation.

hobbitalastair/backhand,hobbitalastair/backhand