Document about parent command injection in subcommands

[Hritik14]

I was looking for ways to access parent flags and got confused with the example on the README which uses a Context to achieve this.
Found an issue which states this more clearly: #121 (comment)

Currently: https://github.com/alecthomas/kong?tab=readme-ov-file#attach-a-run-error-method-to-each-command

type Context struct {
  Debug bool
}
// ...
var cli struct {
  Debug bool `help:"Enable debug mode."`

  Rm RmCmd `cmd:"" help:"Remove files."`
  Ls LsCmd `cmd:"" help:"List paths."`
}

func main() {
  ctx := kong.Parse(&cli)
  err := ctx.Run(&Context{Debug: cli.Debug})

Wouldn't it make more sense to put it like mentioned in the linked issue

type CLI struct {
  Debug bool `help:"Enable debug mode."`

  Rm RmCmd `cmd:"" help:"Remove files."`
  Ls LsCmd `cmd:"" help:"List paths."`
}
// ...
func (l *LsCmd) Run(cli *CLI) error {
// use cli.Debug here !!
  fmt.Println("ls", l.Paths)
  return nil
}

func main() {
  var cli CLI
  ctx := kong.Parse(&cli)
  err := ctx.Run()

this highlights that calling ctx.Run() without arguments makes CLI available inside Run