Add OHF logo to README (#519)

README.md

@@ -66,3 +66,5 @@ Example manifest:
 ## Development
 
 Run `script/develop`. This starts a server. Open it on http://localhost:5001.
+
+[![ESPHome - A project from the Open Home Foundation](https://www.openhomefoundation.org/badges/esphome.png)](https://www.openhomefoundation.org/)