[Changelog] Update Changelog.md to include Swift 5.3 changes

Author: akyrtzi

Changelog.md

@@ -2,6 +2,14 @@
 
 Note: This is in reverse chronological order, so newer entries are added to the top.
 
+## Swift 5.3
+
+* Introduced `FunctionCallExprSyntax.additionalTrailingClosures` property with type `MultipleTrailingClosureElementListSyntax?` for supporting [SE-0279 Multiple Trailing Closures](https://github.com/apple/swift-evolution/blob/master/proposals/0279-multiple-trailing-closures.md).
+
+* Introduced `syntaxNodeType` property for all types conforming to `SyntaxProtocol`, which returns the underlying syntax node type. It is primarily intended as a debugging aid during development.
+
+* Provided a clearer error message for the "parser compatibility" error.
+
 ## Swift 5.2
 
 - `ReversedSyntaxChildren` has been removed