fix: update to prevent regular m.social.image to be displayed in regular chat

proposals/MSCZZZZ-matrix-for-the-social-media-use-case.md

@@ -158,6 +158,8 @@ to previously sended post.
 Defining separate types help making sure the app displaying them
 is able to support all the content of this specific event type.
 
+See the later point for regular room message fallback. 
+
 #### Base event
 
 The structure of the event should just be extensible events.
@@ -244,6 +246,7 @@ like :
 {
   "type": "m.social.image",
   "content": {
+    "m.social.image": [
       "m.caption": [
           {
               "m.text": "Tramline in Berlin"
@@ -273,6 +276,7 @@ like :
             "width": 800
         }
       ],
+    ]
   },   
 }
 ```