Add Miscellaneous section.

- You should mention that another primary purpose of [this key combo]/[killing the X server] is to log another user out by killing their graphical session.
- You can use the [:kbd: role](http://sphinx-doc.org/markup/inline.html#role-kbd) to markup a sequence of keystrokes. Grep our source tree for other uses and try to stay consistent with those.
- You should link the words "X server" to a page explaining what the heck that is for people who don't know. This is a good candidate for our :wikipedia: role ([example](https://github.com/seanfisk/mastering-eos/blame/master/manual/contributing/writing-style.rst#L19))