Updates for how to source "mo" and then use it

When you source mo, it adds the "mo" function to the environment.

demo/using-strings

@@ -1,4 +1,7 @@
 #!/bin/bash
+#
+# This example does not source `mo` and is intentionally restricted to
+# variables that are not arrays.
 cd "$(dirname "$0")" # Go to the script's directory
 export TEST="This is a test"
 echo "Your message:  {{TEST}}" | ../mo