add elements in scalal list code example

Example: scala add to list

def::[B >: A](elem: B): List[B]
Adds an element at the beginning of this list.
	elem is the element to prepend.

	returns a list which contains x as first element 
	and which continues with this list. 

Example:
1 :: List(2, 3) = List(2, 3).::(1) = List(1, 2, 3)