[TASK] Add documentation of coding rules

Change-Id: Ieeca80eefbdf39ace2f621e4166d0d1dc8c51f5a
Reviewed-on: http://brateggevoat1/gerrit/1325
Tested-by: Jenkins <jenkins@brateggevoat1.br-automation.co.at>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
Reviewed-by: Wolfgang Seiss <wolfgang.seiss@br-automation.com>
Reviewed-by: Josef Baumgartner <josef.baumgartner@br-automation.com>