configuration: add note that changes to trunks need a restart

Change-Id: I06e3f8fed9a6784be773fbdd6a1e3d6b41f7b0bb
diff --git a/doc/manuals/chapters/configuration.adoc b/doc/manuals/chapters/configuration.adoc
index 8b8e3bf..1d273b6 100644
--- a/doc/manuals/chapters/configuration.adoc
+++ b/doc/manuals/chapters/configuration.adoc
@@ -53,4 +53,7 @@
 <2> Hide SSRC changes
 <3> Ensure RTP timestamp is aligned with frame duration
 
+NOTE: Changes to trunks that affect resource allocation, such as newly created
+trunks or a change of the number of available endpoints, require a full restart
+of osmo-mgw!