Soil - moisture (#418)

* updated servo calibrator

* updated plot analog pin example

* updated servo example

* first drop of soil moisture

* updated picture

* fixing macros

* update code section

* 5 seconds

* adding soil moisture

* fixing links

docs/examples/plot-analog-pin.md

@@ -1,10 +1,18 @@
 # Plot Analog Pin
 
+Use this program to graph the analog value on pin ``P0``, ``P1`` or ``P2``.
+Press ``A`` to scroll the value on the screen.
+
 ```blocks
+let reading = 0
 basic.forever(() => {
+    reading = pins.analogReadPin(AnalogPin.P0)
     led.plotBarGraph(
-        pins.analogReadPin(AnalogPin.P0),
+        reading,
         1023
     )
+    if (input.buttonIsPressed(Button.A)) {
+        basic.showNumber(reading)
+    }
 })
 ```