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/SUMMARY.md

@@ -19,6 +19,10 @@
     * [Guitar](/projects/guitar)
     * [Duct tape wallet](/projects/wallet)
     * [Watch](/projects/watch)
+    * [Soil Moisture](/projects/soil-moisture)
+    * [Voting Machine](/projects/voting-machine)
+    * [Infection](/projects/infection)
+    * [Fireflies](/projects/fireflies)
     * [Inchworm](/projects/inchworm)
     * [Milk Carton Robot](/projects/milk-carton-robot)
     * [Milk monster](/projects/milky-monster)