[DOCS] Add sponsorship button (#1854)

docs/README.md

@@ -56,6 +56,13 @@ Under the hood, OpenMQTTGateway offers features such as:
 * Over the air updates
 * Local or cloud, your choice
 
+## Using OpenMQTTGateway ?
+Support open-source development through sponsorship and gain exclusive access to our private forum. Your questions, issues, and feature requests will receive priority attention, plus you'll gain insider access to our roadmap.
+
+<div style="text-align: center;">
+    <iframe src="https://github.com/sponsors/theengs/button" title="Sponsor Theengs" height="32" width="228" style="border: 0; border-radius: 6px;"></iframe>
+</div>
+
 ## Products powered by OpenMQTTGateway
 
 ### Theengs Bridge, BLE gateway with external antenna