[12.0][IMP] kpi_dashboard: Add demo data and testing

kpi_dashboard/README.rst

@@ -45,6 +45,18 @@ Configure KPIs
    #. Meter: result must contain `value`, `min` and `max`
    #. Graph: result must contain a list on `graphs` containing `values`, `title` and `key`
 
+#. In order to compute the KPI you can use a predefined function from a model or
+   use the code to directly compute it.
+
+Using KPI with code
+~~~~~~~~~~~~~~~~~~~
+
+Define the code directly on the code field. You can use:
+
+* `self` and `model` as the kpi element
+* The script should create a variable called `result` as a dictionary that
+  will be stored as the value
+
 
 Configure dashboards
 ~~~~~~~~~~~~~~~~~~~~