Add fact that & is commutative

The fact that intersection and union type operators are commutative is important. Therefore I propose to also add it to the overview page for intersection types.

Author: DaniRey

docs/docs/reference/new-types/intersection-types.md

@@ -29,6 +29,8 @@ The members of an intersection type `A & B` are all the members of `A` and all
 the members of `B`.  For instance `Resettable & Growable[String]`
 has member methods `reset` and `add`.
 
+`&` is _commutative_: `A & B` is the same type as `B & A`.
+
 If a member appears in both `A` and `B`, its type in `A & B` is the intersection
 of its type in `A` and its type in `B`. For instance, assume the definitions: