fix: Provide remainder of necessary code. 01_When.md (Kotlin#66)

Provide remainder of necessary code for secondary example to run.

Author: mlb-

examples/02_control_flow/01_When.md

@@ -60,6 +60,8 @@ fun whenAssign(obj: Any): Any {
     }
     return result
 }
+
+class MyClass
 ```
 
 </div>