docs/sp_SP: Warn of links pointing to documentation in English

By default, links in translated Spanish documentation redirect to
documents in English, even if their corresponding Spanish version
exists.

Warn readers about this beforehand through disclaimer.rst.

Signed-off-by: Avadhut Naik <avadhut.naik@amd.com>
Reviewed-by: Carlos Bilbao <carlos.bilbao@amd.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20231211023730.2026204-4-avadhut.naik@amd.com