Add link to the GerritHub migration slides

Change-Id: Ia02418b0a3f000cb0eb5670ba6bc0c290b13dee7
diff --git a/sessions/gerrithub-2.15-upgrade.md b/sessions/gerrithub-2.15-upgrade.md
index 6d195c6..95a3c18 100644
--- a/sessions/gerrithub-2.15-upgrade.md
+++ b/sessions/gerrithub-2.15-upgrade.md
@@ -16,4 +16,6 @@
 - Post-upgrade metrics
 - Retrospective after 6 months on Gerrit 2.15/NoteDb
 
+Replay [slides](https://www.slideshare.net/lucamilanesio/gerrithub-a-true-gerrit-migration-story-to-v215)
+
 *[Luca Milanesio, Gerrit Maintainer - GerritForge Ltd](../speakers.md#lmilanesio)*