[RH199] A note about kill -1

https://role.rhu.redhat.com/rol-rhu/rhz/rhls/course/rh199-7/ch06

It is probably worth noting (in a warning bubble or something) in a part which describes usage of numerical signal values as arguments to kill that "kill -1" has a very special behaviour which could be especially disastrous in scripts, when authors write something like "kill -1 $PID", e.g. without quoting the last argument; I would suggest using "kill -s 1" instead or advising on avoiding numerical values altogether as non-portable (even considering that SIGHUP has the same value on each Linux-supported architecture).