doc: add suricata-update to intro for rules

doc/userguide/rules/intro.rst

@@ -2,12 +2,12 @@ Rules Format
 ============
 
 Signatures play a very important role in Suricata. In most occasions
-people are using existing rulesets. The most used are `Emerging
-Threats <http://www.emergingthreats.net/>`_, `Emerging Threats Pro
-<http://www.emergingthreatspro.com/>`_ and Sourcefire's `VRT
-<http://www.snort.org/vrt/>`_. A way to install rules is described in
-:doc:`../rule-management/oinkmaster`.  This Suricata Rules document explains all about
-signatures; how to read, adjust and create them.
+people are using existing rulesets.
+
+The official way to install rulesets is described in :doc:`../rule-management/suricata-update`.
+
+This Suricata Rules document explains all about signatures; how to
+read, adjust and create them.
 
 A rule/signature consists of the following: