Add Ledger Account Descriptions

As somebody who is relatively new to accounting having a basic description for each account created in the default chart of accounts would be helpful. I'd also suggest moving this section to the "Basics" section in the sidebar as knowing what each account is intended to do should go a long way to getting new users (like myself) up to speed! :)

Start by locating the documentation section for the default chart of accounts and the current sidebar entry. Add a basic description for each account and move this material to the Basics section; done means every default account is explained and the sidebar places the content under Basics.

Written by the indexing model from the issue text.