Link to the Object class reference on the Object class page

People who end up on this page from a search engine might be confused
as to where they can find the Object class reference.

development/cpp/object_class.rst

@@ -3,6 +3,11 @@
 Object class
 ============
 
+.. seealso::
+
+    This page describes the C++ implementation of objects in Godot.
+    Looking for the Object class reference? :ref:`Have a look here. <class_Object>`
+
 General definition
 ------------------