Add release note for deprecated IncrementalEdit

Author: kimdv

Release Notes/600.md

@@ -140,6 +140,11 @@
   - Description: `ByteSourceRange` is being dropped for `Range<AbsolutePosition>`, where the latter clearly signifies that it uses UTF-8 byte positions. `Range<AbsolutePosition>` has deprecated compatibility layers to make it API-compatible with `ByteSourceRange`
   - Pull request: https://github.com/apple/swift-syntax/pull/2587
 
+- `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
 
 - `MacroDefinition` used for expanding macros: