Update snippet descriptions

snippets/symmetricDifference.md

@@ -5,7 +5,8 @@ tags: array,math,intermediate
 
 Returns the symmetric difference between two arrays, without filtering out duplicate values.
 
-- Create a `Set` from each array, then use `Array.prototype.filter()` on each of them to only keep values not contained in the other.
+- Create a `new Set()` from each array to get the unique values of each one.
+- Use `Array.prototype.filter()` on each of them to only keep values not contained in the other.
 
 ```js
 const symmetricDifference = (a, b) => {