Add Custom User-Agent Header Support (#4)

* Add Custom User-Agent Header Support

* Update Readme

* Remove spaces

Author: andrefpoliveira

README.md

@@ -28,6 +28,7 @@ This documentation is for the new Mollie's SDK. You can find more details on how
   * [SDK Example Usage](#sdk-example-usage)
   * [Authentication](#authentication)
   * [Idempotency Key](#idempotency-key)
+  * [Add Custom User-Agent Header](#add-custom-user-agent-header)
   * [Available Resources and Operations](#available-resources-and-operations)
   * [Retries](#retries)
   * [Error Handling](#error-handling)
@@ -242,6 +243,24 @@ print("Payments are the same" if payment1.id == payment2.id else "Payments are d
 ```
 <!-- End Idempotency Key -->
 
+<!-- Start Add Custom User-Agent Header -->
+
+## Add Custom User-Agent Header
+The SDK allows you to append a custom suffix to the `User-Agent` header for all requests. This can be used to identify
+your application or integration when interacting with the API, making it easier to track usage or debug requests. The suffix is automatically added to the default User-Agent string generated by the SDK. You can add it when creating the
+client:
+
+```py
+client = ClientSDK(
+    security = Security(
+        api_key = os.getenv("CLIENT_API_KEY", "test_..."),
+    ),
+    custom_user_agent = "insert something here"
+)
+```
+
+<!-- End Add Custom User-Agent Header -->
+
 <!-- Start Available Resources and Operations [operations] -->
 ## Available Resources and Operations
 
@@ -723,4 +742,4 @@ looking for the latest version.
 While we value open-source contributions to this SDK, this library is generated programmatically. Any manual changes added to internal files will be overwritten on the next generation. 
 We look forward to hearing your feedback. Feel free to open a PR or an issue with a proof of concept and we'll do our best to include it in a future release. 
 
-### SDK Created by [Speakeasy](https://www.speakeasy.com/?utm_source=mollie-api-python-beta&utm_campaign=python)
+### SDK Created by [Speakeasy](https://www.speakeasy.com/?utm_source=mollie-api-python-beta&utm_campaign=python)