Updated Swedish translation
Document keyboard shortcuts

Added a page to list the keyboard shortcuts, according to the code:
https://git.gnome.org/browse/epiphany/tree/src/ephy-window.c#n102

The added page is linked to the first section 'Getting started' of
the index page.

Bugzilla link: https://bugzilla.gnome.org/show_bug.cgi?id=730503