Adds documentation about lack of support for varying element types

Author: skttl

docs/developers-guide.md

@@ -93,6 +93,8 @@ The **Doc Type Grid Editor** supports 3 config options, all of which are optiona
 
 By default, a universal grid editor allowing all available element document types is added upon installation.
 
+Since Doc Type Grid Editor does not support culture variation, element document types allowing culture variations is not available for use in Doc Type Grid Editor.
+
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 ### Hooking Up The Doc Type Grid Editor