[API Doc] Add description and link to UI usage doc for modules

[API Doc] Add description and link to UI usage doc for modules

This is just a minor inconvenience that could easily help when using the ZohoBooks API.

Can we get a short description coming from  https://www.zoho.com/ca/books/help/ that helps understand what each module is for within the Books ecosystem, or at least get a direct link to the help page for that module?

I would think it's not much but it would help for developers new to Books to get a better understanding of what each module is designed for which use-case, which would reduce the risks of errors in early application workflow analysis.

Thanks!