Add note to _.createCallback docs.

Former-commit-id: 0e5dfa9b4dc9aeea1c821b47d2f3d755678ea1aa

dist/lodash.underscore.js

@@ -3399,6 +3399,9 @@
    * If `func` is an object, the created callback will return `true` for elements
    * that contain the equivalent object properties, otherwise it will return `false`.
    *
+   * Note: All Lo-Dash methods, that accept a `callback` argument, internally
+   * use `_.createCallback`.
+   *
    * @static
    * @memberOf _
    * @category Functions