doc/lua: small update to the usage intro

doc/userguide/lua/lua-usage.rst

@@ -1,17 +1,18 @@
 Lua usage in Suricata
 =====================
 
-Lua can be used in two components of Suricata. First one is output an the second one in signature.
+Lua scripting can be used in two components of Suricata. The first is in
+output an the second one in rules in the detection engine.
 
-Both features are using a list of functions to access to data extracted by Suricata. You can get the
-list of functions in the :ref:`lua-functions` page.
+Both features are using a list of functions to access to data extracted by
+Suricata. You can get the list of functions in the :ref:`lua-functions` page.
 
 Lua output
 ----------
 
 Lua can be used to write arbitrary output. See :ref:`lua-output` for more information.
 
-Lua signature
+Lua detection
 -------------
 
-Lua script can be used as a filter in signatures. See :ref:`lua-scripting` for more information.
+Lua script can be used as a filter condition in signatures. See :ref:`lua-scripting` for more information.