docs/sp_SP: Add process email-clients translation

Translate the following document into Spanish:

- process/email-clients.rst

Signed-off-by: Carlos Bilbao <carlos.bilbao@amd.com>
Link: https://lore.kernel.org/r/20230117144722.31195-1-carlos.bilbao@amd.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>