Update union-types.md

This is not very readable, "A union type `A | B` has as values all values".
So update it.

Author: liang3zy22

docs/_docs/reference/new-types/union-types.md

@@ -4,7 +4,7 @@ title: "Union Types"
 nightlyOf: https://docs.scala-lang.org/scala3/reference/new-types/union-types.html
 ---
 
-A union type `A | B` has as values all values of type `A` and also all values of type `B`.
+A union type `A | B` includes all values of both types.
 
 
 ```scala