data: Redirect ContentType assignment to wiki page

Change-Id: Ied40e45296fb25b7efd227e2e13a2af48223bc4b
diff --git a/data.rst b/data.rst
index c6b4d59..39be231 100644
--- a/data.rst
+++ b/data.rst
@@ -55,6 +55,9 @@
 | NACK            | 3              | application-level NACK                                       |
 +-----------------+----------------+--------------------------------------------------------------+
 
+Other ContentType numbers are assigned and maintained in `NDN Packet Specification Wiki <https://redmine.named-data.net/projects/ndn-tlv/wiki/ContentType>`__.
+
+
 FreshnessPeriod
 +++++++++++++++