Add documentation for xfce-helpers scripts
## Submitted by Kevin Bowen `@kevinbowen`
Assigned to **Kevin Bowen `@kevinbowen`**
**[Link to original bug (#16248)](https://bugzilla.xfce.org/show_bug.cgi?id=16248)**
## Description
Add information under development tools https://docs.xfce.org/contribute/dev/start regarding use of xfce-helpers scripts used to working with xfce repos https://github.com/ochosi/xfce-helpers/
issue