Comments/note/document that attaches to the workbook?

I'm not sure how to describe this: Does Smartsheet offer any kind of a comments/note/document that attaches itself to the workbook, instead of a specific row? 

Here's why I ask: I would like a "How to use this sheet" document (standard work) that explains what the sheet is, best practices for how the team should use it, a color key (we use different colored boxes for different people), etc. I don't want to attach it to a specific row (as they fluctuate), or link it to another spreadsheet or have stuff in the row discussions. Does anyone know?

If it does not exist, then for those looking for improvement suggestions, it would be best if it was attached to the dropdown box on the tab. : ) 

Thanks in advance for any ideas!

Beth