docs: pdfdocs: Preserve inter-phrase space in Korean translations

In Korean typesetting, inter-phrase spaces in Hangul text have
a similar role as the the inter-word spaces in Latin text.
They can be preserved by the \xeCJKsetup{CJKspace=true} option.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Link: https://lore.kernel.org/r/68de2e52-e6d1-3f01-c097-15ba7b28a319@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>