chore: added //sampleStart & //sampleEnd (Kotlin#76)

Author: martin-schulte

examples/05_Collections/13_max.md

@@ -7,11 +7,13 @@
 ```kotlin
 fun main() {
 
+//sampleStart
     val numbers = listOf(1, 2, 3)
     val empty = emptyList<Int>()
 
     println("Numbers: $numbers, min = ${numbers.min()} max = ${numbers.max()}") // 1
     println("Empty: $empty, min = ${empty.min()}, max = ${empty.max()}")        // 2
+//sampleEnd
 }
 ```