Add link to git-toprepo presentation material

Change-Id: I5cf54bb6aa69260dfa2b88fe1346394360b421fd

sessions/git-toprepo.md

diff --git a/sessions/git-toprepo.md b/sessions/git-toprepo.md
index 00c72b4..4b44b57 100644
--- a/sessions/git-toprepo.md
+++ b/sessions/git-toprepo.md
@@ -1,10 +1,14 @@
 # git-toprepo - Monorepo when your company won't let you
 
-git-toprepo combines git-submodules on server side and a monorepo client side.
+[Presentation material](https://docs.google.com/presentation/d/1_rkB04jxcaYA1pb-NXFOEgQC0TKHGBemYIrUb-AKCF4)
+
+[git-toprepo] combines git-submodules on server side and a monorepo client side.
 By using Gerrit's submodule tracking, the projects are kept separate on the
 server while the developers experience the ease of git in a single (mono)
 repository.
 
+[git-toprepo]: https://github.com/meroton/git-toprepo
+
 On the client side, users can make a single commit over multiple projects and
 perform cross project git-rebase, git-merge and git-bisect. In Gerrit, the
 developers review and submit cross-project changes using topics.