A membrane switch is nothing more than a regular switch. (with a "moderate" ON resistance)
So you can read it like any other pushbutton. i.e. connect common to GND, the switch to a pin. use pinMode(button, INPUT_PULLUP);
If you have a matrix keypad, you would use exactly the same code as a 4x4 keypad.
You do not need any external electronics.
If you are very tight for pins, you can use an Analog input pin to read 3 or 4 pins on a resistance ladder. But it is a bit unreliable with dirty membrane.
Note to self:
NEVER reply to user c0rsa1r.
He/she doesn't appreciate help if offered, and doesn't want others to learn from their mistakes.