Document that s3.regionEndpoint requires a transport scheme

The `regionEndpoint` value does not work at all without one, so
provide a nice hint that it is required in the vendor-provided
materials.

Fixes Issue: #97

Author: nisimond

values.yaml

@@ -97,7 +97,7 @@ secrets:
 # Options for s3 storage type:
 # s3:
 #  region: us-east-1
-#  regionEndpoint: s3.us-east-1.amazonaws.com
+#  regionEndpoint: https://s3.us-east-1.amazonaws.com
 #  bucket: my-bucket
 #  rootdirectory: /object/prefix
 #  encrypt: false