Add train branch for dashboard-selenium image

Related-prod: PRODX-980
Change-Id: If17fe7e8cbcccc3290a7f94c1dbf4dbaef06b190
diff --git a/Dockerfile b/Dockerfile
index c011b22..efb07ee 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,3 +1,4 @@
+#Dockerfile of branch mcp/train
 ARG FROM=ubuntu:bionic
 FROM $FROM