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/projects/soil-moisture/connect.md

@@ -0,0 +1,49 @@
+# Connect
+
+We are going to use radio to send the current moisture
+level to a dashboard @boardname@. The dashboard
+will display one LED per @boardname@.
+
+## Moisture sensor
+
+To make it happen, we need to change the program to 
+* setup the radio by choosing group 4 and sending the serial number of the device
+* send the moisture level **divided by 4** 
+as the dashboard takes values between ``0`` and ``255``.
+
+```blocks
+radio.setTransmitSerialNumber(true)
+radio.setGroup(4)
+led.setBrightness(64)
+let reading = 0
+basic.forever(() => {
+    pins.analogWritePin(AnalogPin.P1, 1023)
+    reading = pins.analogReadPin(AnalogPin.P0)
+    radio.sendNumber(reading / 4);
+    pins.analogWritePin(AnalogPin.P1, 0)
+    led.plotBarGraph(
+        reading,
+        1023
+    )
+    if (input.buttonIsPressed(Button.A)) {
+        basic.showNumber(reading)
+    }
+    basic.pause(5000);
+})
+```
+
+## The dashboard
+
+The dashboard code can be found at [/examples/radio-dashboard](/examples/radio-dashboard).
+
+Download the code from that example into the @boardname@ that will be used to display the result.
+
+When the dashboard receives a message from a @boardname@, it find a pixel for that board (and remembers it)
+and uses the number received as the brightness of the LED.
+
+When a message hasn't been received by a board for some time, it's pixel will start to blink. After more time, it will simply turn off. 
+
+
+```package
+radio
+```