Add comment explaining overrides and gjs/gts options

lib/config/recommended.js

@@ -19,6 +19,15 @@ module.exports = {
   rules,
 
   overrides: [
+    /**
+     * We don't want to *always* have the preprocessor active,
+     * it's only relevant on gjs and gts files.
+     *
+     * Additionally, we need to declare a global (which is private API)
+     * so that ESLint doesn't report errors about the variable being undefined.
+     * While this is true, it's a temporary thing for babel to do further processing
+     * on -- and isn't relevant to user-land code.
+     */
     {
       files: ['**/*.gjs', '**/*.gts'],
       processor: 'ember/<template>',