docs: Add user guide for Collapse a Message.

templates/zerver/help/collapse-a-message.md

@@ -0,0 +1,22 @@
+### Collapse a message
+
+![collapsed message](/static/images/help/collapsed_message.png)
+
+Zulip allows you to collapse messages to reduce message clutter.
+
+You can do this by simply hovering your mouse over the message,
+pressing the down chevron button
+![down chevron](/static/images/help/down_chevron.png)
+near the upper right corner and selecting **Collapse**.
+
+![collapse message](/static/images/help/collapse_a_message.png)
+
+### Uncollapse a message
+
+![uncollapsed message](/static/images/help/uncollapsed_message.png)
+
+To uncollapse a message, simply press the **[More...]** hyperlink or
+press the down chevron button near the
+upper right corner and selecting **Uncollapse**.
+
+![uncollapse message](/static/images/help/uncollapse_a_message.png)

templates/zerver/help/index.md

@@ -65,7 +65,7 @@ as a “**realm**”.
 * [View information about a message](/help/message-info)
 * [View the exact time a message was sent](/help/message-exact-time)
 * [View an image at full size](/help/image-full-size)
-* Collapse a message
+* [Collapse a message](/help/collapse-a-message)
 * Star a message
 * Share a message or conversation (permanent link)
 ### Editing