Add go:generate for helpgen

This adds a go:generate comment to controller-gen's entrypoint to
generate help, so we should just be able to run go:generate to
regenerate.

Author: DirectXMan12

cmd/controller-gen/main.go

@@ -33,6 +33,8 @@ import (
 	"sigs.k8s.io/controller-tools/pkg/webhook"
 )
 
+//go:generate go run ../helpgen/main.go paths=../../pkg/... generate:headerFile=../../boilerplate.go.txt,year=2019
+
 // Options are specified to controller-gen by turning generators and output rules into
 // markers, and then parsing them using the standard registry logic (without the "+").
 // Each marker and output rule should thus be usable as a marker target.

cmd/helpgen/main.go

@@ -204,7 +204,7 @@ func (Generator) Help() *markers.DefinitionHelp {
 }
 
 func usage() {
-	fmt.Fprintln(os.Stderr, "usage: help-gen generate:headerFile=./hack/boilerplate.go.txt,year=2019 paths=./pkg/...")
+	fmt.Fprintf(os.Stderr, "usage: %s generate:headerFile=./boilerplate.go.txt,year=2019 paths=./pkg/...\n", os.Args[0])
 
 	optInfo := help.ByCategory(optionsRegistry, help.SortByOption)
 	for _, cat := range optInfo {