Documentation for premium HTML template

I am planning to release an HTML template which i have been working on for last few days. While going through a marketplace’s guidelines i came to know that we need to add documentation to final project folder.

Can someone please tell me what kind of documentation it is and how to prepare it? A demo project file would be of great help.

Don’t the guidelines tell you what’s required? If not, they don’t deserve to be called guidelines. There’s no universal rule for what documentation should look like. Short of any concrete rules, my advice would be to explain your software as clearly as you can!