Add comment about adding sections/keys if they don't already exist.

ctrl/modopts.ini

@@ -4,6 +4,8 @@
 ; Example use of this file (or its children) from a JavaScript module:
 ; var options = load({}, "modopts.js", "modname");
 
+; If you find that an expected section or key is not present, add it.
+
 !include modopts.d/*.ini
 
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