help center: Document notification triggers.

Documents the top checkboxes section for controlling mobile, desktop,
and email notifications.

Fixes #23371.

templates/zerver/help/desktop-notifications.md

@@ -6,6 +6,15 @@ customize whether [stream messages](/help/stream-notifications),
 [mentions](/help/pm-mention-alert-notifications#wildcard-mentions)
 trigger desktop notifications.
 
+{start_tabs}
+
+{settings_tab|notifications}
+
+1. Toggle the checkboxes for **Streams** and **PMs, mentions, and alerts**
+   in the **Desktop** column of the **Notification triggers** table.
+
+{end_tabs}
+
 ## Notification sound
 
 You can select the sound Zulip uses for audible desktop notifications. Choosing

templates/zerver/help/email-notifications.md

@@ -6,6 +6,15 @@ Zulip can be configured to send message notification emails for [PMs
 and mentions](/help/pm-mention-alert-notifications), as well as
 [stream messages](/help/stream-notifications).
 
+{start_tabs}
+
+{settings_tab|notifications}
+
+1. Toggle the checkboxes for **Streams** and **PMs, mentions, and alerts**
+   in the **Email** column of the **Notification triggers** table.
+
+{end_tabs}
+
 You can [respond to Zulip messages directly][reply-from-email] by
 replying to message notification emails, unless you are connecting to
 a self-hosted Zulip server whose system administrator has not

templates/zerver/help/mobile-notifications.md

@@ -4,8 +4,16 @@ You can customize whether [stream messages](/help/stream-notifications),
 [private messages](/help/pm-mention-alert-notifications) and
 [mentions][notifications-wildcard-mentions] trigger notifications in Zulip's
 [Android](https://zulip.com/apps/ios) and [iOS](https://zulip.com/apps/ios)
-apps. You can also adjust whether notifications will be sent while you are
+apps.
-online.
+
+{start_tabs}
+
+{settings_tab|notifications}
+
+1. Toggle the checkboxes for **Streams** and **PMs, mentions, and alerts**
+   in the **Mobile** column of the **Notification triggers** table.
+
+{end_tabs}
 
 [notifications-wildcard-mentions]: /help/pm-mention-alert-notifications#wildcard-mentions