Document breaking changes and new OpenAPI support

Updated CHANGELOG to include breaking changes and feature support for OpenAPI 3.2.0.

Author: baywet

CHANGELOG.md

@@ -7,6 +7,10 @@
 
 * adds support for OpenAPI 3.2.0
 
+> Note: Please refer to the [upgrade guide](https://github.com/microsoft/OpenAPI.NET/blob/main/docs/upgrade-guide-3.md) for a detailed description of the breaking changes.
+
+> Note: ASP.net users should remain on version 1.X for ASP.net < 10, and version 2.X for ASP.net 10, this new major version will be implemented in a future version of ASP.net, [more information](https://github.com/microsoft/OpenAPI.NET/blob/main/CONTRIBUTING.md#branches-and-support-policy)
+
 ### Features
 
 * adds support for OpenAPI 3.2.0 ([765a8dd](https://github.com/microsoft/OpenAPI.NET/commit/765a8dd4d6efd1a31b6a76d282ccffa5877a845a))