add more concrete examples of how to use chrt(1)

add more concrete examples of how to use chrt(1)

I've come looking at this manpage with the simple "how do I make this
process use realtime scheduling?" question and couldn't find a
definite answer. Of course, RT is more complicated than "just make
this real time": there's various queues and scheduling classes, but I
think it's worth giving a good, simple example that should basically
work.

In particular, my use case was "my audio is stuttering, is this a
scheduling problem?" By picking the RR scheduler, we set a realtime
scheduling priority that's lower than kernel threads (e.g. migration
is FF/99, irq is FF/50) so that we go above existing processes, but
without kicking out more critical systems.

This, of course, is a matter of taste, and the settings here are a
little arbitrary. I send this patch in the hope that either those are
accepted as canon (which would surprise me) or that someone comes up
with a more canonical example.

The "reset" example also seems like a more critical addition to the
manual.

Finally, I change the name of the section from USAGE to the more
standard EXAMPLES, as per man-pages(7).