Add release note for deprecated IncrementalEdit

Author: kimdv

Release Notes/601.md

@@ -6,6 +6,11 @@
 
 ## Deprecations
 
+- `IncrementalEdit` deprecated in favor of `SourceEdit`
+  - Description: `IncrementalEdit` is being dropped for `SourceEdit`. `SourceEdit` has deprecated compatibility layers to make it API-compatible with `IncrementalEdit`
+  - Issue: https://github.com/apple/swift-syntax/issues/2532
+  - Pull request: https://github.com/apple/swift-syntax/pull/2604
+
 ## API-Incompatible Changes
 
 ## Template