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

union.js

@@ -11,6 +11,7 @@ import isArrayLikeObject from './isArrayLikeObject.js';
  * @category Array
  * @param {...Array} [arrays] The arrays to inspect.
  * @returns {Array} Returns the new array of combined values.
+ * @see unionBy, unionWith, difference, without, xor, xorBy
  * @example
  *
  * union([2], [1, 2]);