Add completion script

command/completion.go

@@ -0,0 +1,41 @@
+package command
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+var shellType string
+
+func init() {
+	RootCmd.AddCommand(completionCmd)
+	completionCmd.Flags().StringVarP(&shellType, "shell", "s", "bash", "The type of shell")
+}
+
+var completionCmd = &cobra.Command{
+	Use:    "completion",
+	Hidden: true,
+	Short:  "Generates completion scripts",
+	Long: `To enable completion in your shell, run:
+
+  eval "$(gh completion)"
+
+You can add that to your '~/.bash_profile' to enable completion whenever you
+start a new shell.
+
+When installing with Homebrew, see https://docs.brew.sh/Shell-Completion
+`,
+	RunE: func(cmd *cobra.Command, args []string) error {
+		switch shellType {
+		case "bash":
+			RootCmd.GenBashCompletion(os.Stdout)
+		case "zsh":
+			RootCmd.GenZshCompletion(os.Stdout)
+		default:
+			return fmt.Errorf("unsupported shell type: %s", shellType)
+		}
+		return nil
+	},
+}