[Geary] feedback on help pages

[fede inventati org]

I see that you didn't fix this string:

To set preferences in Geary, open the application menu or click the gear 
menu at the upper right of the toolbar and choose 
<gui>Preferences</gui>.


Also, I cannot reproduce what is described here:

To permanently delete the conversations, hold down <key>Shift</key> and 
press the <gui>Delete</gui> button that appears in place of the 
<gui>Trash</gui> button.

If I hold Shift the button doesn't change (tested also on english 
locale).