Gentoo specific directories

The main Gentoo specific directories mentioned in the Gentoo Handbook.

External resources

 * https://devmanual.gentoo.org/general-concepts/filesystem/index.html - General concepts from the Dev Handbook for Gentoo developers on filesystem hierarchy.
 * https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard - Wikipedia's article on the Linux Filesystem Hierarchy Standard (FHS).