Index.rst: added best practice 'Central configure values'

extension/Documentation/UsersManual/Index.rst

@@ -2868,8 +2868,23 @@ Relation: `Person.id = Address.personId`
 
 
 
-Best Practise: Chart
-====================
+Best Practise
+=============
+
+Central configured values
+-------------------------
+
+Any variable in *config.qfq.ini* can be used by *{{<varname>:Y}}* in form or report statements.
+
+E.g.
+
+  TECHNICAL_CONTACT = jane.doe@example.net
+
+Could be used in an *FormElement*.type = sendmail with *parameter*  setting *sendMailFrom={{TECHNICAL_CONTACT:Y}}*.
+
+
+Chart
+-----
 
 * QFQ delivers a chart JavaScript lib: https://github.com/nnnick/Chart.js.git. Docs: http://www.chartjs.org/docs/
 * The library is not sourced in the HTML page automatically. To do it, either include the lib