add 'device chat about' to now existing status (#2613)

the 'device chat about' was shown as a single message
as at that time, there was just not 'status'.

meanwhile, we have the status option,
and it feels much more natural to get the information there,
esp. as the subtitle on all UIs already read
'Messages in this chat are generated locally' -
and a tap on that will show the hint, without scrolling or so.

this also teaches the user where to find such information -
and the "welcome" chat is less spammy and really starts with the text
"Welcome to Delta Chat!"

src/contact.rs

@@ -218,6 +218,7 @@ impl Contact {
         } else if contact_id == DC_CONTACT_ID_DEVICE {
             contact.name = stock_str::device_messages(context).await;
             contact.addr = DC_CONTACT_ID_DEVICE_ADDR.to_string();
+            contact.status = stock_str::device_messages_hint(context).await;
         }
         Ok(contact)
     }