DOC: Update Object::AddObserver documentation

The Command objects are derived from Object therefore SmartPointers
are used.

Author: blowekamp

Modules/Core/Common/include/itkObject.h

@@ -145,14 +145,14 @@ class ITKCommon_EXPORT Object : public LightObject
     SetGlobalWarningDisplay(false);
   }
 
-  /** Allow people to add/remove/invoke observers (callbacks) to any ITK
-   * object. This is an implementation of the subject/observer design
+  /** \brief Add an observer/command to this object invoked for event
+   *
+   * This is an implementation of the subject/observer design
    * pattern. An observer is added by specifying an event to respond to
    * and an itk::Command to execute. It returns an unsigned long tag
    * which can be used later to remove the event or retrieve the
-   * command.  The memory for the Command becomes the responsibility of
-   * this object, so don't pass the same instance of a command to two
-   * different objects  */
+   * command.
+   */
   unsigned long
   AddObserver(const EventObject & event, Command *);
   unsigned long