[LTP] [PATCH] doc: add `--recurse-submodules` when cloning the repo

[Petr Vorel]

Hi all,

> Hi!
> > User could run syscalls testing suite with
> > `./kirk -f ltp -r syscalls`,
> > but they may not be aware of the submodule `kirk`.
> > So I add the `--recurse-submodules` option.

thanks, merged!

Kind regards,
Petr