Move old shell/main to subdirectory

Also update README reference to same

_examples/shell/commandstring/main.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"fmt"
+	"github.com/alecthomas/kong"
+)
+
+var cli struct {
+	Debug bool `help:"Debug mode."`
+
+	Rm struct {
+		User      string `help:"Run as user." short:"u" default:"default"`
+		Force     bool   `help:"Force removal." short:"f"`
+		Recursive bool   `help:"Recursively remove files." short:"r"`
+
+		Paths []string `arg:"" help:"Paths to remove." type:"path" name:"path"`
+	} `cmd:"" help:"Remove files."`
+
+	Ls struct {
+		Paths []string `arg:"" optional:"" help:"Paths to list." type:"path"`
+	} `cmd:"" help:"List paths."`
+}
+
+func main() {
+	ctx := kong.Parse(&cli,
+		kong.Name("shell"),
+		kong.Description("A shell-like example app."),
+		kong.UsageOnError(),
+		kong.ConfigureHelp(kong.HelpOptions{
+			Compact: true,
+			Summary: true,
+		}))
+	switch ctx.Command() {
+	case "rm <path>":
+		fmt.Println(cli.Rm.Paths, cli.Rm.Force, cli.Rm.Recursive)
+
+	case "ls":
+	}
+}