docs: Add user guide for *Add custom emoji* feature.

templates/zerver/help/add-custom-emoji.md

@@ -0,0 +1,58 @@
+# Add custom emoji
+
+If you are an administrator of a Zulip organization, you can add custom emojis
+to your organization for other members to use.
+
+1. Click the cog (![cog](/static/images/help/cog.png)) in the upper right corner
+of the right sidebar.
+
+2. Select **Administration** from the dropdown menu that appears.
+
+    ![Administration dropdown](/static/images/help/administration.png)
+
+3. Upon clicking **Administration**, your view will be replaced with the
+**Administration** page. You will be located on the **Organization settings**
+tab by default.
+
+    ![Administration page](/static/images/help/admin-window.png)
+
+4. Scroll down to the **Custom emoji** section located beneath the
+**Organization settings** section.
+
+    ![Custom emoji](/static/images/help/custom-emoji.png)
+
+5. In the green section labeled **Add a New Emoji**, find the **Emoji name** and
+**Emoji URL** fields.
+
+    * In the **Emoji name** field, enter a phrase for your emoji. Only alphanumeric characters, dashes, and underscores are allowed, but dashes and underscores cannot end an emoji phrase.
+
+        ![Emoji name](/static/images/help/emoji-name.png)
+
+        Users will use the designated emoji phrase surrounded by colons to
+        insert your emoji into their messages.
+
+    * In the **Emoji URL** field, insert the link to your custom emoji's image. The
+    link must start with **http://** or **https://**.
+
+        ![Emoji URL](/static/images/help/emoji-url.png)
+
+        Please note that the image will be scaled down to 25x25 pixels in users' messages.
+
+6. After filling out the **Emoji name** and **Emoji URL** fields, click the blue
+**Add emoji** button to add your custom emoji to your Zulip organization.
+
+    ![Add emoji](/static/images/help/add-emoji.png)
+
+7. Upon clicking the **Add emoji** button, you will receive a notification
+labeled **Custom emoji added!** in the **Add a New Emoji** section, confirming
+the success of the addition of your custom emoji to your organization.
+
+    ![Custom emoji success](/static/images/help/custom-emoji-success.png)
+
+    The emoji's information and settings will also be displayed above the
+    **Add a New Emoji** section. You can choose to delete any custom emojis in
+    your organization through this panel.
+
+8. Users in your organization can now use your emoji in their messages.
+
+    ![Custom emoji demo](/static/images/help/custom-emoji-demo.png)

templates/zerver/help/index.md

@@ -135,7 +135,7 @@ as a “**realm**”.
 * Only allow admins to create new streams
 * [Restrict editing of old messages and topics](/help/restrict-editing-of-old-messages-and-topics)
 * [Change the default language for realm](/help/change-the-default-language-for-realm)
-* Add custom emoji
+* [Add custom emoji](/help/add-custom-emoji)
 * Configure authentication methods
 * Add a custom linkification filter
 * Delete your organization (not implemented)