fix layouting bug in section 6.10

fix layouting bug in section 6.10

As visible on the i3wm.org-website, the layout in 6.10 is a bit weird.
The command "xrandr --output […]" is not displayed as a command (i.e.
terminal-style), but as regular text, the text accompanying it before
instead is displayed as a command.

This leads to other weird behaviour:
The following section "move window|container to mark <mark>" starts a
new chapter, which I don't think it should, and its accompanying
description is displayed a commands.

Since I don't know how to build this website, this fix might not even
fix it, and it is most certainly not tested. I apologize for that and
strongly second #39.