Add links for downTo and step in Kotlin ranges

Updated the control flow documentation to include links for 'downTo' and 'step' functions.

Author: kanedazz

docs/topics/tour/kotlin-tour-control-flow.md

@@ -271,9 +271,9 @@ The most common way to create a range in Kotlin is to use the `..` operator. For
 
 To declare a range that doesn't include the end value, use the `..<` operator. For example, `1..<4` is equivalent to `1, 2, 3`.
 
-To declare a range in reverse order, use `downTo`. For example, `4 downTo 1` is equivalent to `4, 3, 2, 1`.
+To declare a range in reverse order, use [`downTo`](https://kotlinlang.org/api/core/kotlin-stdlib/kotlin.ranges/down-to.html). For example, `4 downTo 1` is equivalent to `4, 3, 2, 1`.
 
-To declare a range that increments in a step that isn't 1, use `step` and your desired increment value.
+To declare a range that increments in a step that isn't 1, use [`step`](https://kotlinlang.org/api/core/kotlin-stdlib/kotlin.ranges/step.html) and your desired increment value.
 For example, `1..5 step 2` is equivalent to `1, 3, 5`.
 
 You can also do the same with `Char` ranges: