user docs: Document auto-numbering of ordered lists.

Fixes #8246

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

@@ -75,6 +75,12 @@ to include lists in your messages.
     You can add nested bullets within lists by adding two spaces before each
     nested bullet.
 
+Numbered lists in which each item begins with the same number will
+have the numbers automatically edited to increment (e.g. if every line
+starts with `3.`, it'll go 3, 4, 5, ...).
+
+![Numbered lists](/static/images/help/numbered-lists-screenshot.png)
+
 ## Emojis
 
 Zulip features a variety of emojis provided by the

templates/zerver/markdown_help.html

@@ -49,6 +49,16 @@
                             </ul>
                         </td>
                     </tr>
+                    <tr>
+                        <td>1. Milk<br/>
+                            1. Tea<br/>
+                            1. Coffee
+                        </td>
+                        <td>1. Milk<br/>
+                            2. Tea<br/>
+                            3. Coffee
+                        </td>
+                    </tr>
                     <tr>
                         <td>:heart: (and <a href="http://www.emoji-cheat-sheet.com/" target="_blank">many others</a>, from the <a href="https://code.google.com/p/noto/" license="/static/generated/emoji/images/emoji/NOTICE" target="_blank">Noto Project</a>)</td>
                         <td><img alt=":heart:" class="emoji" src="/static/generated/emoji/images/emoji/heart.png" title=":heart:" /></td>