Merge pull request #1480 from ember-cli/bmish-docs-optional-rule-example-readme

Update optional rule example to use actual optional rule

Author: lin-ll

README.md

@@ -36,8 +36,8 @@ module.exports = {
     'plugin:ember/recommended' // or other configuration
   ],
   rules: {
-    // override rule settings here
-    'ember/no-jquery': 'error'
+    // override / enable optional rules
+    'ember/no-replace-test-comments': 'error'
   }
 };
 ```