board: freescale: t208xrdb: Add link to User Guide

The User Guide contains handy things like block diagrams and DIP switch
settings and it's even available on the public web. Add a link to it in
the README.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
diff --git a/board/freescale/t208xrdb/README b/board/freescale/t208xrdb/README
index 9e4b28f..ec47c96 100644
--- a/board/freescale/t208xrdb/README
+++ b/board/freescale/t208xrdb/README
@@ -34,6 +34,11 @@
  - Support for hardware virtualization and partitioning enforcement
  - QorIQ Platform's Trust Architecture 2.0
 
+User Guide
+----------
+The T2080RDB User Guide is available on the web at
+https://www.nxp.com/docs/en/user-guide/T2080RDBPCUG.pdf
+
 Differences between T2080 and T2081
 -----------------------------------
   Feature		T2080	 T2081