Copyright headers

cmd/tk/bootstrap.go

cmd/tk/bootstrap_github.go

cmd/tk/bootstrap_gitlab.go

cmd/tk/check.go

cmd/tk/completion.go

cmd/tk/create.go

cmd/tk/create_kustomization.go

cmd/tk/create_source.go

cmd/tk/create_source_git.go

cmd/tk/delete.go

cmd/tk/delete_kustomization.go

cmd/tk/delete_source.go

cmd/tk/delete_source_git.go

cmd/tk/export.go

cmd/tk/export_kustomization.go

cmd/tk/export_source.go

cmd/tk/export_source_git.go

cmd/tk/flags.go

cmd/tk/get.go

cmd/tk/get_kustomization.go