Payroll feature is already there in Book Keeper as of now.
Check out payroll feature in details:
If you don't want to use payroll and instead want to maintain manual entries,
You can create a salary account under Indirect Expenses
Account can be easily created under All Accounts
After creating an account, please record an Expense Transaction under Transactions > Expense > Create
In Paid from : Select Cash or Bank
In Paid to : Select Salary account which you just created under Indirect Expenses.