[DOCS] Add sponsorship button (#1854)

docs/participate/support.md

@@ -8,3 +8,9 @@ If you like the project and/or used it please consider supporting it! It can be
 * Buy devices, boards or parts from the [compatible web site](https://compatible.openmqttgateway.com), the devices and parts linked use affiliated links.
 * Donate or sponsor the project [developers](https://github.com/1technophile/OpenMQTTGateway/graphs/contributors)
 * Make a video or a blog article about what you have done with [OpenMQTTGateway](https://docs.openmqttgateway.com) and share it.
+
+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>