updates: Add update message (level=14).

help/line-spacing.md

@@ -1,9 +1,10 @@
 # Line spacing
 
-Zulip lets you adjust line spacing in the web and desktop apps, to make the UI
-feel comfortable for you. Most importantly, this setting modifies how much space
-there is between lines of text in multi-line messages. You can experiment to see
-what configuration makes reading most pleasant for you.
+Zulip lets you adjust line spacing in the web and desktop apps, to
+make the Zulip interface feel most comfortable for you. Most
+importantly, this setting modifies how much space there is between
+lines of text in multi-line messages. You can experiment to see what
+configuration makes reading most pleasant for you.
 
 Reducing line spacing and [font size](/help/font-size) may be helpful on small
 screens, so that you can see more content at a time.

zerver/lib/zulip_update_announcements.py

@@ -340,6 +340,18 @@ quickly insert them into the message you're composing.
             private_channels_url="/help/channel-permissions#private-channels",
         ),
     ),
+    ZulipUpdateAnnouncement(
+        level=14,
+        message="""
+**Web and desktop updates**
+- You can now choose from a wide range of [font size]({font_size_url})
+and [line spacing]({line_spacing_url}) options, to make the Zulip interface
+feel most comfortable for you.
+""".format(
+            font_size_url="/help/font-size",
+            line_spacing_url="/help/line-spacing",
+        ),
+    ),
 ]