docs(readme): correct Ginkgo path in tools example

Resolves #703

README.md

@@ -93,7 +93,7 @@ Create (or update) a file called `tools/tools.go` with the following contents:
 package tools
 
 import (
-	_ "github.com/onsi/ginkgo"
+	_ "github.com/onsi/ginkgo/ginkgo"
 )
 
 // This file imports packages that are used when running go generate, or used