(docs) add message-failure slot

Author: antoine92190

README.md

@@ -702,6 +702,7 @@ Example:
 | `room-header-info`                  | Replace the template of the room header text                | `room`, `typingUsers`, `userStatus` |
 | `room-options`                      | Replace the template of the room options                    | -                                   | menu-icon                                                                                                          |
 | `message`                           | Replace the template of the message box                     | `message`                           | `deleted-icon`, `eye-icon`, `document-icon`, `pencil-icon`, `checkmark-icon`, `dropdown-icon`, `emoji-picker-icon` |
+| `message-failure`                   | Replace the message failure icon                            | -                                   | -                                                                                                                  |
 | `messages-empty`                    | Replace the empty message template                          | -                                   | -                                                                                                                  |
 | `rooms-empty`                       | Replace the empty rooms template                            | -                                   | -                                                                                                                  |
 | `no-room-selected`                  | Replace the no room selected template                       | -                                   | -                                                                                                                  |