Add link to PNOR Code Update repo

Added implementation link to
https://github.com/openbmc/openpower-pnor-code-mgmt

Change-Id: I3c2405faa8e92eab88cea64645d1a420ebf840a0
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/code-update/host-code-update.md b/code-update/host-code-update.md
index fa382a0..3f6d267 100644
--- a/code-update/host-code-update.md
+++ b/code-update/host-code-update.md
@@ -131,3 +131,7 @@
 Information about associations, the MANIFEST file, deleting an image, software
 field mode, and software factory reset can be found at
 [ubi-code-update.md#associations](ubi-code-update.md#associations)
+
+### Implementation
+
+https://github.com/openbmc/openpower-pnor-code-mgmt