document that esp32 uses different pins

[joshua-8]

• update pins in the code if the first esp32 go baby go car uses different pins for a good reason
• update documentation for which pins the esp32 uses

///// joystick reader pins /////
byte JOY_X_PIN = 39;  // Analog input pin that the left-right potentiometer is attached to
byte JOY_Y_PIN = 35;  // Analog input pin that the forwards-backwards potentiometer is attached to

///// drive controller pins /////
byte LEFT_MOTOR_CONTROLLER_PIN = 18;
byte RIGHT_MOTOR_CONTROLLER_PIN = 21;

byte SPEED_KNOB_PIN = 33;

byte BUTTON_MODE_PIN = 23; // can turn button control mode on and off