[Documentation]: intro tutorial bugs

[bendichter]

What would you like changed or added to the documentation and why?

• Formatting in Processing background section
• Add new attributes to Subject

Do you have any interest in helping write or edit the documentation?

Yes.

Code of Conduct

• I agree to follow this project's Code of Conduct
• Have you checked the Contributing document?
• Have you ensured this change was not already requested?

[rly]

Also would be nice to print the expandable nwbfile in the read section.