doc/userguide: explain --strict-rule-keywords

doc/userguide/partials/options.rst

@@ -48,6 +48,7 @@
    flow state between files.
 
 .. option:: --pcap-file-recursive
+
    Used with the -r option when the path provided is a directory.  This option
    enables recursive traversal into subdirectories to a maximum depth of 255.
    This option cannot be combined with --pcap-file-continuous.  Symlinks are
@@ -153,6 +154,20 @@
 
    Exit with a failure when errors are encountered loading signatures.
 
+.. option:: --strict-rule-keywords[=all|<keyword>|<keywords(csv)]
+
+   Applies to: classtype, reference and app-layer-event.
+
+   By default missing reference or classtype values are warnings and
+   not errors. Additionally, loading outdated app-layer-event events are
+   also not treated as errors, but as warnings instead.
+
+   If this option is enabled these warnings are considered errors.
+
+   If no value, or the value 'all', is specified, the option applies to
+   all of the keywords above. Alternatively, a comma separated list can
+   be supplied with the keyword names it should apply to.
+
 .. option:: --disable-detection
 
    Disable the detection engine.