Adjust to the new titlebar buttons of GNOME Disks

This is actually a good news because the new button is much harder to
confuse with the double gear button for partition.

We're now supporting three generations of GNOME Disks...

wiki/src/install/linux/usb.mdwn

@@ -44,15 +44,24 @@
 
    <div class="step-image">[[!img install/inc/infography/install-intermediary-tails.png link="no" alt=""]]</div>
 
-1. Click on the [[!img lib/emblem-system.png alt="System" class="symbolic" link="no"]]
+1. Click on the [[!img lib/open-menu.png alt="Menu" class="symbolic" link="no"]]
    button in the titlebar and choose <span class="guimenuitem">Restore Disk Image&hellip;</span>.
 
+   [[!img install/inc/screenshots/gnome_disks_menu.png class="screenshot" link="no" alt=""]]
+
+   If your version of <span class="application">GNOME Disks</span> is
+   old it might have a [[!img lib/emblem-system.png alt="System" class="symbolic" link="no"]]
+   button instead. Click on the [[!img lib/emblem-system.png alt="System" class="symbolic" link="no"]]
+   button and choose <span class="guimenuitem">Restore Disk
+   Image&hellip;</span>.
+
    [[!img install/inc/screenshots/gnome_disks_system.png class="screenshot" link="no" alt=""]]
 
    <div class="bug">
 
-   <p>If your version of <span class="application">GNOME Disks</span> is old
-   and has no [[!img lib/emblem-system.png alt="System" class="symbolic" link="no"]]
+   <p>If your version of <span class="application">GNOME Disks</span> is even older
+   and has neither a [[!img lib/open-menu.png alt="Menu" class="symbolic" link="no"]]
+   nor a [[!img lib/emblem-system.png alt="System" class="symbolic" link="no"]]
    button, you have to [[!toggle id="dd" text="install an intermediary Tails
    using the command line"]].</p>