[Bug 1087697] man page inaccuracy about --sig-proxy and --tty

[Red Hat Bugzilla]

https://bugzilla.redhat.com/show_bug.cgi?id=1087697

--- Comment #11 from Lukas Doktor  ---
Well I disagree. I just tried the reproducer on docker-1.2.0-19.el7.x86_64 and
-SIGUSR didn't generate any output, -2 killed the process. The only proxified
signal were the one I generated using keyboard (ctrl+z, ctrl+c). But when I use
`kill -... $PID` the signal is processed only by the attach process and is not
forwarded.

With --tty=true it works fine.