Add map exercise code

Author: kobelavaerts

exercises/01_building_blocks/operator_map.nf

@@ -0,0 +1,11 @@
+#!/usr/bin/env nextflow
+
+Channel
+    .of( 1, 2, 3, 4, 5 )
+    .map { it * it }
+    .subscribe onNext: { println it }, onComplete: { println 'Done' }
+
+// Channel
+//     .of( 1, 2, 3, 4, 5 )
+//     .map { it * it }
+//     .view()