Add coral-edgetpu-stable source.

Change-Id: Ie7f4da68952aacf4bfd3c5498e4c1665a1a953bc
diff --git a/multistrap.conf b/multistrap.conf
index 97492d4..21c7d99 100644
--- a/multistrap.conf
+++ b/multistrap.conf
@@ -15,3 +15,8 @@
 packages=
 source=https://packages.cloud.google.com/apt
 suite=mendel-bsp-enterprise-beaker
+
+[coral]
+packages=
+source=https://packages.cloud.google.com/apt
+suite=coral-edgetpu-stable