I just reset my iPhone 5 and I can't set it up. It's asking for a sim card

The iPhone needs to have a sim card installed to activate. Did you remove the sim card it had?

Or have you not added a sim card yet?

To open the tray use a sim tool, or a paper clip and press in oon the sim eject pin hole on the side of the iPhone:

Make sure a Sim card is installed there.

You need a SIM card in the phone to activate it. The SIM does not have to be one that is currently tied to an account, it can be an expired SIM. But it must be for the carrier the phone is SIM locked to, if it is SIM locked.

Put a SIM in it... A SIM is required to activate the phone.