Update 04-layout-of-the-MarcEditor.md

Added instructor notes. The notes in lesson 4 could use more detail if someone with a Mac could investigate the differences between the MarcEditor top level menu in PC vs Mac

Author: abigailsparling

episodes/04-layout-of-the-MarcEditor.md

@@ -28,6 +28,11 @@ The MarcEditor has a robust set of features available via the top level menu. Fe
 
 ![](fig/topLevelFeatures_marcEditor.png){alt='MarcEdit top level menu'}
 
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+Note: A number of differences have been noted in the MarcEditor Top Level Menu design and features for Mac users in this lesson.
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 ### MarcEditor Top Level Menu Features
 
 Each top level menu heading contains many options. Below are some highlights of those features that are frequently used when working with a set of MARC data.