Make better documentation for nmcli, NetworkManager Keyfiles

tl;dnr: If you want people to adopt new tech that is WILDLY different from old tech, document the bajeebus out of it with lots of examples...

Do a page search for 'keyfile' on the RHEL 7 networking guide. You'll get one hit, and not a relevant one.

https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html-single/Networking_Guide/index.html

The guide only discusses ifcfg-rh which is a legacy transition tool at best - the official docs should do better than that.

The Fedora docs have a bit better coverage of keyfiles:

http://fedoraproject.org/wiki/Networking/Bridging#Using_configuration_files_.28keyfile.29

...but if you want to be real about it, even that documentation kind of sucks because it doesn't provide a solid practical example. Had to find one in the comments of a bugreport of all places (via google):

https://bugzilla.redhat.com/show_bug.cgi?id=1080643#c1

Just a complaint about the state of RHEL 7 docs in a couple places.