Add more guid documentation

ObjectMethods.h

@@ -153,6 +153,13 @@ namespace LuaObject
     /**
      * Returns the GUID of the [Object].
      * 
+     * GUID is an unique identifier for the object.
+     * 
+     * However on MaNGOS and cMangos creatures and gameobjects inside different maps can share
+     * the same GUID but not on the same map.
+     * 
+     * On TrinityCore this value is unique across all maps
+     *
      * @return uint64 guid
      */
     int GetGUID(Eluna* /*E*/, lua_State* L, Object* obj)
@@ -164,8 +171,12 @@ namespace LuaObject
     /**
      * Returns the low-part of the [Object]'s GUID.
      * 
-     * This is the counter that is unique among [Object]s of the same type
+     * On TrinityCore all low GUIDs are different for all objects of the same type.
-     *   (e.g. no two [Creature]s will have a low-GUID of 5 at the same time).
+     * For example creatures in instances are assigned new GUIDs when the Map is created.
+     * 
+     * On MaNGOS and cMaNGOS low GUIDs are unique only on the same map.
+     * For example creatures in instances use the same low GUID assigned for that spawn in the database.
+     * This is why to identify a creature you have to know the instanceId and low GUID. See [Map:GetIntstanceId]
      *
      * @return uint32 guidLow
      */