I'm assuming that you can do most of creating the PID loop, and only need help with the specific setting minimum and maximum speeds. If this is the case, you'll need to run the following method in the constructor of the Subsystem, where "pid" is the PID Controller.
Code:
pid.setOutputRange(minimumOutput, maximumOutput);
If you're using a PID Subsystem, you would just call setOutputRange in the constructor of the class.