help: Offer links to "Message formatting" for logged in users.

- Replaces instructions for opening the message formatting reference
  with `{relative|gear|message-formatting}`.

help/format-your-message-using-markdown.md

@@ -130,10 +130,13 @@ A summary of the formatting syntax above is available in the Zulip app.
 
 {start_tabs}
 
-{!start-composing.md!}
+{relative|gear|message-formatting}
 
-1. Click the **question mark** (<i class="fa fa-question"></i>) icon at the
-   bottom of the compose box.
+!!! tip ""
+
+    You can also [open the compose box](/help/open-the-compose-box), and click
+    the **question mark** (<i class="fa fa-question"></i>) icon at the bottom of
+    the compose box.
 
 {end_tabs}
 

zerver/lib/markdown/help_relative_links.py

@@ -27,6 +27,7 @@ gear_info = {
     "billing": ["Billing", "/billing/"],
     "invite": ["Invite users", "/#invite"],
     "keyboard-shortcuts": ["Keyboard shortcuts (?)", "/#keyboard-shortcuts"],
+    "message-formatting": ["Message formatting", "/#message-formatting"],
     "about-zulip": ["About Zulip", "/#about-zulip"],
 }