Add benchmark results in a comment at the bottom

raindrops.go

@@ -1,5 +1,3 @@
-// +build !example
-
 package raindrops
 
 import "strconv"
@@ -23,4 +21,7 @@ func Convert(i int) string {
 	return s
 }
 
-// The test program has a benchmark too.  How fast does your Convert convert?
+// Iteration 1 Benchmark
+// PASS
+// BenchmarkConvert-12	 2000000	       676 ns/op
+// ok  	exercism/go/raindrops	2.048s