Add help page for font embedding in document file. The property
was introduced in release 4.1 by tdf#42195
Copyedit welcome.
Change-Id: I265ead91ffba632450169a424b122a21a17eb56c
Reviewed-on: https://gerrit.libreoffice.org/22025
Reviewed-by: Olivier Hallot <ohallot@collabora.co.uk>
Tested-by: Olivier Hallot <ohallot@collabora.co.uk>