message: tools: add pip install instructions
diff: @@ -35,6 +35,9 @@ command -v protoc-gen-mavsdk > /dev/null || {
  echo >&2 "'protoc-gen-mavsdk' not found in PATH"
  echo >&2 ""
  echo >&2 "Make sure 'protoc-gen-mavsdk' is installed and available"
  + echo >&2 "You can install it using pip:"
  + echo >&2 ""
  + echo >&2 " pip3 install --user protoc-gen-mavsdk"
  exit 1
  }
  