Update the changelog

CHANGELOG.md

@@ -5,6 +5,7 @@
 Enhancements:
 - .NET Standard 2.0 and 2.1 support (@lg2de, #485)
 - Non-intercepted methods on a class proxy with target are now forwarded to the target (@stakx, #571)
+- Significant performance improvements with proxy type generation for interface proxies without target. (Up until now, DynamicProxy generated a separate `IInvocation` implementation type for every single proxied method – it is now able to reuse a single predefined type in many cases, thereby reducing the total amount of dynamic type generation.) (@stakx, #573)
 
 Bugfixes:
 - Proxying certain `[Serializable]` classes produces proxy types that fail PEVerify test (@stakx, #367)