Prepare CHANGELOG for release

CHANGELOG.md

@@ -1,11 +1,11 @@
 # Release History
 
-## 2.0.0-beta.1 (Unreleased)
+## 2.0.0-beta.1 (2024-06-06)
 
 ### Features Added
 
-### Breaking Changes
+This is the official OpenAI client library for C# / .NET. It provides convenient access to the OpenAI REST API from .NET applications and supports all the latest features. It is generated from our [OpenAPI specification](https://github.com/openai/openai-openapi) in collaboration with Microsoft.
 
-### Bugs Fixed
+### Breaking Changes
 
-### Other Changes
+If you are a user migrating from version 1.11.0 or earlier, consider checking out our [migration guide]() to help you get started.