doc: update to include additional rule references

Signed-off-by: jason taylor <jtfas90@gmail.com>

diff --git a/doc/userguide/rules/intro.rst b/doc/userguide/rules/intro.rst
index 07fc3fde2169a2d035c25045f8494ae10fd65ea3..e5b92b5449cf99ae526df5784996e35856f5aee3 100644 (file)
--- a/doc/userguide/rules/intro.rst
+++ b/doc/userguide/rules/intro.rst
@@ -6,6 +6,10 @@ people are using existing rulesets.
 
 The official way to install rulesets is described in :doc:`../rule-management/suricata-update`.
 
+There are a number of free rulesets that can be used via suricata-update.
+To aid in learning about writing rules, the Emerging Threats Open ruleset
+is free and a good reference that has a wide range of signature examples.
+
 This Suricata Rules document explains all about signatures; how to
 read, adjust and create them.