Your bump map is set up correctly. If you .png image has built in alpha channel, connect it like this (make sure to change blend mode away from opaque):
The other method you have heard of involves connecting a Transparent BSDF and a separate BSDF (such as diffuse) through a mix shader, and connecting the the alpha channel as a mix factor. However, this is not necessary with a Principled BSDF, as it has a transparency channel built in that is controlled automatically by the alpha input.