quick docs menu addition and fixes

[Matthew Miller]

Hey, can someone review (and hopefully, merge) these:

https://pagure.io/fedora-docs/quick-docs/pull-request/324
https://pagure.io/fedora-docs/quick-docs/pull-request/325

The first one makes the left menu better by splitting up the "Usage and
Customization" category on what seems to me to be natural break: about half
of them were about adding software or otherwise using repos and packages.

The second fixes some punctuation, moves the Dracut docs to Kernel and
booting, and puts Postgres next to MySQL/MariaDB.