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)
+    }
 })
 ```

docs/examples/servo-calibrator.md

@@ -1,14 +1,21 @@
 # Servo calibrator
 
+Use this program to calibrate the angles of a servo.
+Press ``A`` to reduce the angle by 5 and ``B`` to
+increase it by 5.
+
+The current angle is displayed on the screen
+in a loop.
+
 ```blocks
 let angle = 90
 input.onButtonPressed(Button.A, () => {
-    angle -= 5
+    angle -= Math.max(0, 5)
     pins.servoWritePin(AnalogPin.P0, angle)
     led.stopAnimation()
 })
 input.onButtonPressed(Button.B, () => {
-    angle += 5
+    angle += Math.min(180, 5)
     pins.servoWritePin(AnalogPin.P0, angle)
     led.stopAnimation()
 })
@@ -16,5 +23,4 @@ basic.forever(() => {
     basic.showNumber(angle)    
 })
 pins.servoWritePin(AnalogPin.P0, angle)
-basic.showString("Press A or B to change servo angle")
 ```