How to show internal pullups on a schematic?

there is no need to show the pullups, your code will explain the fact that the pullups are used in the mcu. if you want to show someone how to build it why show them stuff they are not assembling ? that is on the coding side. Anyone that clever seeing a button from the input to ground will probably know that it is connected to an internal pull up else it would be pretty pointless having a button that just goes to ground.