Add doc note to _.isEqual about not supporting comparing DOM nodes or functions. [ci skip]

lodash.js

@@ -6198,6 +6198,11 @@
      * by the method instead. The callback is bound to `thisArg` and invoked
      * with two arguments; (value, other).
      *
+     * Note: This method supports comparing arrays, booleans, `Date` objects,
+     * numbers, `Object` objects, regexes, and strings. Functions and DOM nodes
+     * are **not** supported. A callback may be used to extend support for
+     * comparing other values.
+     *
      * @static
      * @memberOf _
      * @category Objects