doc: add upgrade note about suricatasc and suricatactl

doc/userguide/upgrade.rst

@@ -98,6 +98,11 @@ Major changes
 - If the configuration value ``ftp.memcap`` is invalid, Suricata will set it to ``0`` which means
   no limit will be placed. In previous Suricata  releases, Suricata would terminate execution. A
   warning message will be displayed `Invalid value <value> for ftp.memcap` when this occurs.
+- The utility applications ``suricatasc`` and ``suricatactl`` have
+  been rewritten in Rust. For most end-users this is a transparent
+  change, however if you run these tools from the source directory,
+  patch them or use them as Python modules your workflows may need to
+  be adapted.
 
 Removals
 ~~~~~~~~