Add Q_DECLARE_METATYPE(Post*) to the example (#60)

doc/table.md

@@ -50,6 +50,9 @@ public:
     explicit Post(QObject *tableSet = 0);
 
 };
+
+Q_DECLARE_METATYPE(Post*)
+
 ```
 
 ## Declare child table
@@ -67,4 +70,4 @@ Post::Post(QObject *parent) : Table(parent),
 }
 ```
 
-For more example take a look at _tests/common_ folder
+For more example take a look at _tests/common_ folder