message: adding badge of nightly build
diff: </p>
  ![CI Build](https://github.com/bark-simulator/bark/workflows/CI/badge.svg)
  +![NIGHTLY Build](https://github.com/bark-simulator/bark/workflows/NIGHTLY/badge.svg)
  # BARK - a tool for **B**ehavior benchm**Ark**ing
  BARK provides a semantic simulation tool/framework for autonomous agents with a special focus on autonomous driving.
  