Update README.md

Author: alex-makarov

README.md

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 # hoverboard-driver
+![main workflow](https://github.com/alex-makarov/hoverboard-driver/actions/workflows/main.yml/badge.svg)
+
 ROS hardware driver for UART-controlled hoverboard. Can be used with [diff_drive_controller](http://wiki.ros.org/diff_drive_controller). Hoverboard is using modified [firmware](https://github.com/alex-makarov/hoverboard-firmware-hack-FOC) by [Emanuel Feru](https://github.com/EmanuelFeru), changed to report wheel odometry via serial protocol.
 
 If you're looking for the version of Hoverboard driver for