You have to create your own .conf file in bitcoin roaming folder. The path will be : C:\Users\Username\AppData\Roaming\Bitcoin
Just create a file named settings.conf in here and it should pick that up.
It is better to name the file bitcoin.conf so that you don't need to specify -conf=<file> when running your bitcoin qt IMO.
Yeah, sure name whatever you like i was just giving the idea how to do that.