forbid starting `$` char in ```sh code blocks

sometimes we put, sometimes not - we can add lint rule to always avoid
<img width="362" alt="image" src="https://user-images.githubusercontent.com/7361780/234560678-93c9acda-9355-476a-9840-e29e714a33fa.png">
<img width="291" alt="image" src="https://user-images.githubusercontent.com/7361780/234560717-1006b7ff-34f6-4161-b6a4-a83e2bca6385.png">
