Add types in the Kleisli code sample for composition (#2165)

This makes it easier for the reader to follow the flow of the types.

docs/src/main/tut/datatypes/kleisli.md

@@ -77,11 +77,14 @@ Returning to our earlier example:
 // Bring in cats.FlatMap[Option] instance
 import cats.implicits._
 
-val parse = Kleisli((s: String) => if (s.matches("-?[0-9]+")) Some(s.toInt) else None)
+val parse: Kleisli[Option,String,Int] =
+  Kleisli((s: String) => if (s.matches("-?[0-9]+")) Some(s.toInt) else None)
 
-val reciprocal = Kleisli((i: Int) => if (i != 0) Some(1.0 / i) else None)
+val reciprocal: Kleisli[Option,Int,Double] =
+  Kleisli((i: Int) => if (i != 0) Some(1.0 / i) else None)
 
-val parseAndReciprocal = reciprocal.compose(parse)
+val parseAndReciprocal: Kleisli[Option,String,Double] =
+  reciprocal.compose(parse)
 ```
 
 `Kleisli#andThen` can be defined similarly.