Added explanation for colon character

Use of the colon character for value assignment is now explained by example of function add10.

scala.html.markdown

@@ -104,10 +104,13 @@ val sq = (x:Int) => x * x
 
 sq(10)   // Gives you this: res33: Int = 100.
 
+// The colon explicitly defines the type of a value, in this case a function
+// taking an Int and returning an Int. 
+val add10: Int => Int = _ + 10 
+
 // Scala allows methods and functions to return, or take as parameters, other
 // functions or methods.
 
-val add10: Int => Int = _ + 10 // A function taking an Int and returning an Int
 List(1, 2, 3) map add10 // List(11, 12, 13) - add10 is applied to each element
 
 // Anonymous functions can be used instead of named functions: