adding pins.pulseIn API

docs/reference/pins/pulse-in.md

@@ -0,0 +1,53 @@
+# Pulse In
+
+Returns the duration of a pulse (high or low) from a [pin](/device/pins) on
+the micro:bit board in microseconds.
+
+```sig
+pins.pulseIn(DigitalPin.P0, PulseValue.High)
+```
+
+### ~avatar
+
+Some pins are also used by the [LED screen](/device/screen).
+Please read the [page about pins](/device/pins) carefully.
+
+### ~
+
+### Parameters
+
+* ``name`` is a [string](/reference/types/string) that stores the name of the pin (``P0``, ``P1``, or ``P2``, up through ``P20``)
+* ``value`` is the value of the pulse, ``high`` or ``low``
+
+### Returns
+
+* a [number](/reference/types/number) that represents the pulse duration in micro-seconds
+
+### Example: football score keeper
+
+The following script sends a pulse on ``P0`` and reads the pulse returned by a HC-SR04 sonar to determine the distance of the object in front of the sensor.
+
+```blocks
+basic.forever(() => {
+    // send pulse
+    pins.digitalWritePin(DigitalPin.P0, 0)
+    control.waitMicros(2)
+    pins.digitalWritePin(DigitalPin.P0, 1)
+    control.waitMicros(10)
+    pins.digitalWritePin(DigitalPin.P0, 0)
+
+    // read pulse
+    led.plotBarGraph(pins.pulseIn(DigitalPin.P1, PulseValue.High) / 58, 0)
+    basic.pause(100)
+})
+```
+
+#### ~hint
+
+This function is not supported in the simulator.
+
+#### ~
+
+### See also
+
+[digital write pin](/reference/pins/digital-write-pin),