help: Update documentation for numbered lists.

- Documents the new button in the compose box and the automatic
  numbering when the "Enter" key is pressed.

Fixes #27093.

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

@@ -59,6 +59,12 @@ whenever you need a reminder of the formatting syntax below.
 
 {!numbered-lists-examples.md!}
 
+!!! tip ""
+
+    You can also use the **Numbered list** (<i class="fa fa-list-ol"></i>)
+    button in the compose box to insert numbered list formatting.
+    [Learn more](/help/numbered-lists).
+
 ## Links
 
 {!links-intro.md!}

help/numbered-lists.md

@@ -2,6 +2,39 @@
 
 {!numbered-lists-intro.md!}
 
+## Create a numbered list
+
+{start_tabs}
+
+{tab|via-markdown}
+
+{!start-composing.md!}
+
+1. Type a number followed by a `.` and some text to start a numbered list.
+
+1. Press <kbd>Enter</kbd> to automatically add a new number to the list.
+
+!!! tip ""
+
+    Pressing <kbd>Enter</kbd> on a blank list item will remove the list
+    formatting on the current line.
+
+{tab|via-compose-box-buttons}
+
+{!start-composing.md!}
+
+1. _(optional)_ Select the text you want to format.
+
+1. Click the **Numbered list** (<i class="fa fa-list-ol"></i>) icon at the
+   bottom of the compose box to insert list formatting.
+
+!!! tip ""
+
+    You can also use the **Numbered list** (<i class="fa fa-list-ol"></i>) icon
+    to remove existing list formatting from the current line or selected text.
+
+{end_tabs}
+
 ## Examples
 
 {!numbered-lists-examples.md!}