[kotlin/en] Add small section for lambda functions (#4798)

kotlin.html.markdown

@@ -120,6 +120,13 @@ fun helloWorld(val name : String) {
     println(even(6)) // => true
     println(even(7)) // => false
 
+    /*
+    You can also use lambda functions, with the '->' operator seperating
+    the parameters from the function body.
+    */
+    fun fooLambda: (Int) -> Int = {n -> n + 1}
+    println(fooLambda(1)) // => 2
+
     // Functions can take functions as arguments and return functions.
     fun not(f: (Int) -> Boolean): (Int) -> Boolean {
         return {n -> !f.invoke(n)}