Fix #2208: Add handler configuration documentation (#2221)

* Fix #2208: Add handler configuration documentation

- Add Handler Configuration section to AspNetCoreServer.Hosting README
- Document executable vs class library handler modes
- Explain Main(string[] args) pitfall causing JsonSerializerException
- Provide clear code examples for correct handler setup
- Address community confusion about Lambda handler configuration

* Added change file

* Applied code review feedback

* Applied code review feedback.

* Delete .autover/changes/issue-2208-handler-configuration-docs.json

* Fix: Add missing closing backticks to code block

---------

Co-authored-by: Garrett Beatty <gcbeatty@amazon.com>

Author: jnunn-aws

Libraries/src/Amazon.Lambda.AspNetCoreServer.Hosting/README.md

@@ -50,6 +50,10 @@ app.Run();
 
 ```
 
+## Handler Configuration
+
+The Lambda function handler must be set to the assembly name (e.g., `MyLambdaProject`). The `AddAWSLambdaHosting` method sets up the Lambda runtime client and registers the callback for processing Lambda events, so the handler should not use the class library format (`<assembly-name>::<full-type-name>::<method-name>`).
+
 ## Extension Points
 
 `AddAWSLambdaHosting` accepts an optional `HostingOptions` configuration action that exposes the same customization hooks available in the traditional `AbstractAspNetCoreFunction` base class approach.