Latest changes in gnome-user-docs

Hi all,

while completing the translation of gnome-user-docs, I stumbled upon
this string:

#. (itstool) path: note/p
#: C/files-preview.page:35
#, fuzzy
#| msgid ""
#| "<link style=\"button\" action=\"install:gnome-tweaks\">Install "
#| "<app>Tweaks</app></link>"
msgid ""
"<link style=\"button\" href=\"apt:gnome-sushi\">Install <app>Sushi</app></"
"link>"
msgstr ""
"<link style=\"button\" action=\"install:gnome-tweaks\">Installieren Sie das "
"<app>Optimierungswerkzeug</app></link>"

The "apt" command is usually only available on Debian based systems.
The previous "install" seems to be more generic. This should be
investigated further. Currently (Fedora 27, Gnome 3.26) such an
"install" link attempts to start a PackageKit based software
management. Don't know what happens when such an "apt" link is clicked
in the Yelp window.

Don't forget: there's a world outside the Ubuntu/Debian/Mint microcosm ;)

Best Regards,
Mario