Add _.fill doc example. [ci skip]

lodash.src.js

@@ -4748,6 +4748,19 @@
      * @param {number} [start=0] The start position.
      * @param {number} [end=array.length] The end position.
      * @returns {Array} Returns `array`.
+     * @example
+     *
+     * var array = [1, 2, 3];
+     *
+     * _.fill(array, 'a');
+     * console.log(array);
+     * // => ['a', 'a', 'a']
+     *
+     * _.fill(Array(3), 2);
+     * // => [2, 2, 2]
+     *
+     * _.fill([4, 6, 8], '*', 1, 2);
+     * // => [4, '*', 8]
      */
     function fill(array, value, start, end) {
       var length = array ? array.length : 0;