README refers to invalid status executable

https://gitlab.com/micro-ROS/ros_tracing/ros2_tracing/blob/34450ab575caae38f86a3faf36b66937b2c6952e/README.md#L26

3. Source and check that tracing is enabled:
    ```
    $ source ./install/local_setup.bash
    $ ros2 run tracetools tracetools_status
    ```

It's status, not tracetools_status