help_docs: Document unsubscribe user from stream via profile.

Extends the documentation on unsubscribing users from streams to
include an alternate method via the user's full profile, which
is useful for cases where admins may need to unsubscribe a single
user from multiple streams.

Fixes #21379.

templates/zerver/help/add-or-remove-users-from-a-stream.md

@@ -46,3 +46,25 @@ including streams the admin is not subscribed to.
 {end_tabs}
 
 [configure-invites]: /help/configure-who-can-invite-to-streams
+
+### From a user's profile (alternate method)
+
+This method is useful if you need to remove one user from multiple streams.
+
+{start_tabs}
+
+1. Hover over a user's name in the right sidebar.
+
+1. Click on the ellipsis (<i class="zulip-icon zulip-icon-ellipsis-v-solid"></i>) to
+   the right of their name.
+
+1. Click **View full profile**.
+
+1. Select the **Streams** tab.
+
+1. Under **Subscribed streams**, find the stream you would like
+   to remove the user from.
+
+1. Click the **Unsubscribe** button in that row.
+
+{end_tabs}