Docs/translations/ko_KR: link howto.rst with other language versions

The menu for documents of other available languages is created for
documents in same file hierarchy under the translations/ directory.
Because howto.rst of Korean translation is at the root of translations/
directory while that for English is under howto/ directory, the Korean
translation is not linked with other available language versions via the
menu.  Move the document under the same hierarchy to make it be linked
with other langauge versions.

Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240826010949.78305-1-sj@kernel.org