Add disclaimer that emoji formatting is not relevant in Desired Outcome

Author: khhuang7

flex/07-flex-layout-2/README.md

@@ -20,6 +20,8 @@ On a smaller screen it will look like this:
 
 ![smaller](./desired-outcome-smaller.png)
 
+Note: The emojis may instead show up as one or several text symbols (e.g. ☆♂) if the Noto Color Emoji font family is not properly installed. This does not affect the exercise and can be ignored.
+
 ### Self Check
 - The header text is size 32px and weight 900.
 - The header text is vertically centered and 16px from the edge of the screen.