Add related function for each module. [closes #2932]

flatten.js

@@ -7,6 +7,7 @@ import baseFlatten from './.internal/baseFlatten.js';
  * @category Array
  * @param {Array} array The array to flatten.
  * @returns {Array} Returns the new flattened array.
+ * @see flatMap, flatMapDeep, flatMapDepth, flattenDeep, flattenDepth
  * @example
  *
  * flatten([1, [2, [3, [4]], 5]]);