add badge to readme

.github/workflows/cmake.yml

 # https://github.com/raspberrypi/pico-examples/blob/master/.github/workflows/cmake.yml
 
-name: CMake
+name: Firmware
 on: [push, pull_request]
 
 env:

README.md

 # Pi Pico Volcano Remote Control Gadget
 
+![Firmware](https://github.com/xythobuz/Volcano-Remote/actions/workflows/cmake.yml/badge.svg)
+
 Supports:
 
  * workflows for the Volcano Hybrid