help-docs: Extend notification bot documentation.

Updates the documentation for configuring the notification bot to
include information about the non-configurable messages sent for
stream settings / permissions changes as well as topic resolve
events.

Adds more detailed sections / information about the configurable
aspects of the notification bot, and information about the topics
for the various messages sent by the notification bot.

Fixes #21947.

templates/zerver/help/configure-notification-bot.md

@@ -1,21 +1,74 @@
-# Configure notification bot
+# Notification bot
+
+The Zulip notification bot automatically generates messages for
+various organization level events, including:
+
+* Stream settings changes such as [name](/help/rename-a-stream),
+  [description](/help/change-the-stream-description),
+  [permission](/help/stream-permissions) and
+  [policy](/help/stream-sending-policy) updates (sent to the
+  "stream events" topic)
+* A topic being [resolved/unresolved](/help/resolve-a-topic)
+* New public stream announcements (private streams are not announced)
+* New user announcements
+
+The notification bot also generates messages to individual users
+for some user specific events, such as [being subscribed to a
+stream][add-users-to-stream] by another user.
+
+Organization administrators can configure where (and whether)
+[new stream](#new-stream-notifications) and
+[new user](#new-user-notifications) announcement messages are sent.
+
+Stream messages sent by the notification bot (including the topic)
+are translated into the language that the organization has configured
+as the [organization notifications language][org-notifications-lang].
+Notification bot messages sent to a single user will use
+[their preferred language](/help/change-your-language).
+
+## Configure notification bot
 
 {!admin-only.md!}
 
-The Zulip notification bot sends a message whenever:
+### New stream notifications
 
-* A user joins the organization
-* A new public stream is [announced](/help/create-a-stream#stream-options)
-
-You can configure where those messages are sent, or disable them entirely.
-
-### Configure notification bot
+You can configure where the Zulip notification bot
+[announces][new-stream-options] new public streams, or disable the new
+stream notification messages entirely. The topic for these messages
+is "new streams".
 
 {start_tabs}
 
 {settings_tab|organization-settings}
 
-1. Under **Notifications**, configure
-   **New stream notifications** and **New user notifications**.
+1. Under **Notifications**, configure **New stream notifications**.
+
+{!save-changes.md!}
 
 {end_tabs}
+
+### New user notifications
+
+You can configure where the Zulip notification bot announces new users,
+or disable the new user notification messages entirely. The topic for
+these messages is "signups".
+
+{start_tabs}
+
+{settings_tab|organization-settings}
+
+1. Under **Notifications**, configure **New user notifications**.
+
+{!save-changes.md!}
+
+{end_tabs}
+
+## Related articles
+
+* [Organization notifications language][org-notifications-lang]
+* [Streams and topics](/help/streams-and-topics)
+
+[add-users-to-stream]: /help/add-or-remove-users-from-a-stream#add-users-to-a-stream
+[api-create-user]: https://zulip.com/api/create-user
+[new-stream-options]: /help/create-a-stream#stream-options
+[org-notifications-lang]: /help/change-the-default-language-for-your-organization