connect anemometer to pico

Oh perfect - I didn't look there! So yeah, wiring it up will be trivial.

You could wire to anything but let's say you chose to wire one side to GND and one to B3:

var lastRotation = getTime();
function anemRotated(e) {
  var d = e.time-lastRotation;
  lastRotation = e.time;
  console.log("Speed = "+(60/d)+" rpm");
}
pinMode(B3, "input_pullup"); // activate pullup resistor
setWatch(anemRotated, B3, {repeat:true, edge:"falling"});

You'd need to run something every few seconds that's check whether it had in fact stopped turning, but otherwise that's it...