added documentation for site overlays

Signed-off-by: Christian Goll <cgoll@suse.com>

CHANGELOG.md

@@ -81,6 +81,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Provide detected kernel version to overlay templates. #1556
 - Bump github.com/containers/storage from 1.53.0 to 1.55.2 #1316, #892
 - Process nodes.conf path dynamically from config. #1595, #1596, #1569
+- Split overlays into distribution and site overlays. #831
 
 ### Removed
 

userdocs/contents/overlays.rst

@@ -25,11 +25,17 @@ overlay in two different ways:
 
 The default profile has both a **wwinit** and a **runtime** overlay
 configured.
+Warewulf distinguishes between **distribution** shipped with warewulf
+and **site** overlays which are created by the end user. A **site** takes
+always precedence over a **distribution** overlay with the sane name.
+Any modification of a **distribution** overlay with ``wwctl`` will create
+a **site** overlay with the same name.
+The **site** overlays are place normally under ``/etc/warewulf/overlays``.
 
 Overlays are compiled for each compute node individually.
 
-Provided overlays
-=================
+Provided distribution overlays
+==============================
 
 These overlays are provided as part of Warewulf.