Document default password

Change-Id: I2387450b25c7f5e4dcfabbaa60a9ae719c7b24bb
diff --git a/charts/voltha.md b/charts/voltha.md
index e39a45a..eb7b47a 100644
--- a/charts/voltha.md
+++ b/charts/voltha.md
@@ -73,3 +73,5 @@
 ```shell
 ssh voltha@<pod-ip> -p 30110
 ```
+
+The default VOLTHA password is `admin`.