[Bug]: fix typo in 04_user_guide.md

### Contact Details

_No response_

### Short description of the problem here.

 fix typo in 04_user_guide.md

### CausalNex Version

0.12.1

### Python Version

3.10

### Relevant code snippet

_No response_

### Relevant log output

_No response_

### Code of Conduct

- [X] I agree to follow this project's Code of Conduct