feat: add 'group created instructions' as info message (#4916)

Before, it was shown by UI when the chat is empty, however, in case of
verified groups, this is never the case any longer as the 'e2ee now
guaranteed' is always added.

src/stock_str.rs

@@ -413,6 +413,9 @@ pub enum StockMessage {
 
     #[strum(props(fallback = "%1$s sent a message from another device."))]
     ChatProtectionDisabled = 171,
+
+    #[strum(props(fallback = "Others will only see this group after you sent a first message."))]
+    NewGroupSendFirstMessage = 172,
 }
 
 impl StockMessage {
@@ -1284,6 +1287,11 @@ pub(crate) async fn aeap_explanation_and_link(
         .replace2(new_addr)
 }
 
+/// Stock string: `Others will only see this group after you sent a first message.`.
+pub(crate) async fn new_group_send_first_message(context: &Context) -> String {
+    translated(context, StockMessage::NewGroupSendFirstMessage).await
+}
+
 /// Text to put in the [`Qr::Backup`] rendered SVG image.
 ///
 /// The default is "Scan to set up second device for <account name (account addr)>".  The