Make the ADD_COMMENT example more realistic

hoijui and Michael Muré created 

Co-Authored-By: Michael Muré <batolettre@gmail.com>

Change summary

doc/model.md | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

Detailed changes

doc/model.md 🔗 

@@ -29,8 +29,8 @@ These `Operation`s are aggregated in an `OperationPack`, a simple array. An `Ope
     "author": {
       "id": "5034cd36acf1a2dadb52b2db17f620cc050eb65c"
     },
-    "timestamp": 1533640589,
-    "title": "This title is better"
+    "timestamp": 1533640612,
+    "message": "A new comment"
   }
 ]
 ```