reference INSPIRE technical guidelines in feed export help

Change-Id: I9efee1a5ef6b28effe4f7e14166f18cb13e4e92f
Reviewed-on: http://gerrit.esdi-community.eu/3183
Reviewed-by: Simon Templer <simon.templer@igd.fraunhofer.de>
Tested-by: Simon Templer <simon.templer@igd.fraunhofer.de>