Add link to slides for "Diffy with Enterprise Grade"

Change-Id: I92a74fa9cc295929ec9f1030e84463373ce964f6

sessions/diffy-with-enterprise-grade.md

diff --git a/sessions/diffy-with-enterprise-grade.md b/sessions/diffy-with-enterprise-grade.md
index 274583a..47cef83 100644
--- a/sessions/diffy-with-enterprise-grade.md
+++ b/sessions/diffy-with-enterprise-grade.md
@@ -8,3 +8,5 @@
 implemented on top of vanilla Gerrit.
 
 *[Eryk Szymanski, CollabNet](../speakers.md#eszymanski)*
+
+[Slides](https://www.slideshare.net/eryksz/diffy-with-enterprise-grade)