help: Improve unread count badge documentation.

Also mention it on /help/follow-a-topic.

help/desktop-notifications.md

@@ -36,11 +36,12 @@ You can select the sound Zulip uses for audible desktop notifications. Choosing
 
 ## Unread count badge
 
-By default, Zulip displays how many unmuted unread messages you have
-in the organization on the [desktop app](https://zulip.com/apps/)
-sidebar and on the browser tab icon. You can configure which types of
-messages are included in the count. Choosing **None** disables unread
-count badges.
+By default, Zulip displays a count of your unmuted unread messages on the
+[desktop app](https://zulip.com/apps/) sidebar and on the browser tab icon. You
+can configure the badge to only count [direct messages](/help/direct-messages)
+and [mentions](/help/mention-a-user-or-group), or to include messages in
+[followed topics](/help/follow-a-topic) but not other
+[stream](/help/streams-and-topics) messages.
 
 ### Configure unread count badge
 
@@ -53,6 +54,17 @@ count badges.
 
 {end_tabs}
 
+### Disable unread count badge
+
+{start_tabs}
+
+{settings_tab|notifications}
+
+1. Under **Desktop message notifications**, select **None** from the
+   **Unread count badge** dropdown.
+
+{end_tabs}
+
 ## Troubleshooting desktop notifications
 
 First, make sure you have enabled

help/follow-a-topic.md

@@ -60,6 +60,11 @@ You can use followed topics for a variety of workflows:
 
 ## Configure notifications for followed topics
 
+You can configure custom notifications for followed topics. You can also
+[configure the unread count
+badge](/help/desktop-notifications#unread-count-badge) to include unread
+messages just in followed topics, without counting other stream messages.
+
 {!configure-notifications-for-followed-topics.md!}
 
 ## Automatically follow topics