Add more whats new items in 2.1 (micronaut-projects#4047)

Author: jameskleeh

src/main/docs/guide/introduction/whatsNew.adoc

@@ -2,10 +2,26 @@ Micronaut {version} includes the following changes:
 
 === Core Features
 
+==== Kotlin 1.4
+
+Micronaut now ships with Kotlin 1.4 for those users using Kotlin.
+
 ==== Introspections for JDK 14 Records
 
 It is now possible to define <<introspection, bean introspections>> on JDK 14+ record types (note these currently require the `––enable–preview` flag to the compiler and JVM).
 
+==== Client Binding API
+
+A new API has been created to allow for binding declarative HTTP client method arguments to an HTTP request. See the <<clientParameters, documentation>> for more information.
+
+==== Websocket Improvements
+
+Query parameters are now respected and bindable in the Micronaut websocket support.
+
+==== HttpResponse Improvements
+
+Cookies in HTTP responses from the client side are now retrievable on the HttpResponse. These are the cookies found in the `Set-Cookie` header.
+
 === Module Upgrades
 
 TODO