Update README.md

Author: stephencelis

README.md

@@ -73,7 +73,7 @@ assertSnapshot(matching: vc, as: .image(on: .iPadMini(.portrait)))
 assertSnapshot(matching: vc, as: .recursiveDescription(on: .iPadMini(.portrait)))
 ```
 
-> Note: Snapshots must be compared using a simulator with the same OS, device gamut, and scale as the simulator that originally took the reference to avoid discrepancies between images.
+> ⚠️ Warning: Snapshots must be compared using a simulator with the same OS, device gamut, and scale as the simulator that originally took the reference to avoid discrepancies between images.
 
 Better yet, SnapshotTesting isn't limited to views and view controllers! There are [a number of available snapshot strategies](Documentation/Available-Snapshot-Strategies.md) to choose from.