Add documentation for xfce-test automated scripts

Submitted by Yousuf Philips `@philipzae`

Assigned to Kevin Bowen @kevinbowen

Link to original bug (#16787)

Description

maggotbrain suggested this bug report be filed, as it relates to bug 16249, and info can be pulled from https://github.com/schuellerf/xfce-test

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information