robot-name: Add hints.md file (exercism#858)

This describes the bonus test and how to run it.

closes exercism#832

Author: robphoenix

exercises/robot-name/.meta/hints.md

@@ -0,0 +1,13 @@
+### Bonus exercise
+
+Once you get `go test` passing, try `go test -tags bonus`.  This uses a *build
+tag* to enable a test that wasn't previously enabled. Build tags control which
+files should be included in the package. You can read more about those at [the
+Go documentation](https://golang.org/pkg/go/build/#hdr-Build_Constraints).
+
+For this exercise it limits `go test` to only build the tests in the
+`robot_name_test.go` file. We can then include the bonus test in the
+`bonus_test.go` file with the tags flag as described above.
+
+To get the bonus test to pass you'll have to ensure a robot's name has not been
+used before.

exercises/robot-name/bonus_example.go

@@ -7,6 +7,8 @@ import (
 	"math/rand"
 )
 
+const testVersion = 1
+
 type Robot struct {
 	name string
 }