Update System_Locale_and_Keyboard_Configuration.adoc

I installed fedora with gnome. I wanted to easily change my keyboard layout (a task many people want to do sooner rather than later for obvious reasons). However the instructions were not working and it wasn't until some time later that I realized that gnome was in control of the layout. I still don't know what config file or variable in my system gnome is referring to. However once I knew it was a gnome issue the issue was easily solved.

So if gnome is the 'flagship desktop environment' used on fedora then it makes sense to add instructions while notifying the user that it is more of a gnome issue rather than a fedora issue along with a link of where to find the original instructions from gnome for those who want to learn more or read it from the source.