New virtual server 403 forbidden error - virtualmin isnt adding a default index.html

i have forgotten...what is the procedure for enabling virtualmin to create, and add automatically to any new virtualm server/ public html directory, a default index.html file so this error doesnt appear?

to explain a little further...lets say i have a webhosting business called joes webhosting. If a new hosting client registers a new virtual server from my whmcs interface, i want virtualmin to add a default "joes webhosting" index.html to any new client virtual server webpage. Of course, once the client creates their own website this file would be removed/overwritten.