update release notes

src/docs/releases/2.1.0.md

@@ -4,6 +4,14 @@ Release date: Not yet released
 
 ## Change Logs
 
+### Behavior Change
+
+#### `JsonOptions` Configuration
+
+One of the most significant changes in version 2.0 was the transition from Newtonsoft.Json to System.Text.Json. Initially, we configured the default `JsonOptions` to match the settings we used for serializing documents. However, in this release, we’ve reverted that decision and no longer configure `JsonOptions` by default, allowing you the flexibility to customize it as needed.
+
+If your API returns YesSql documents as JSON (e.g., ContentItem, User, Query, Notification), you may need to use `DocumentJsonSerializerOptions` for accurate serialization. For example, when using Minimal API, instead of returning the result with `TypedResults.Ok(document)`, you should return it using `Results.Json(document, options.Value.SerializerOptions);`, resolving `IOptions<DocumentJsonSerializerOptions>` from the IoC container.
+
 ### Users  Feature
 
 #### External Authentication Logic Has Been Separated From the Users Feature