manual: prepend X11 to description

Clarifying ambiguity of "apropos keyboard". X(7) requests we use the term X11 instead of Xorg, so that's what I've done.

This is 1 of (xor) 2 proposed patches. This is the "minimal change to solve half the problem" commit.

I have a rewritten page in mdoc(7), which provides massively better searching of the manual subsystem. It's mostly the same but I think I've improved some of the language slightly. I don't understand all the makefile macros autogenerating parts of the page, mine is just self-contained, but written nicely. What I don't have is integration with this makefile so that it fills in all these parts. So, if that functionality is desirable I'll need some help. Also I can't figure out how to get gitlab tokens to work with my git. Can I upstream that one instead?

With love from Worthington Ohio, USA, and from FreeBSD.