Add HACKING.rst coding style doc
Add HACKING.rst coding style doc

 * Addresses bug 977685

Change-Id: Id04cad3021f015abe965f79b8930da55e092ada1

dougwig/x-neutron-vpnaas,openstack/neutron-fwaas,citrix-openstack-build/neutron-vpnaas,openstack/networking-odl,gotostack/neutron-lbaas,openstack/networking-odl,mestery/x-stackforge-odl,openstack/neutron-fwaas,gotostack/neutron-lbaas,gaolichuang/neutron-fwaas,gotostack/neutron-lbaas,flavio-fernandes/networking-odl,CiscoSystems/networking-odl,gandelman-a/neutron-lbaas,gaolichuang/neutron-fwaas,openstack/networking-odl,flavio-fernandes/networking-odl,CiscoSystems/networking-odl,FedericoRessi/networking-odl,gandelman-a/neutron-lbaas,FedericoRessi/networking-odl,citrix-openstack-build/neutron-lbaas,openstack/neutron-vpnaas,citrix-openstack-build/neutron-fwaas,gandelman-a/neutron-lbaas,dougwig/x-neutron-fwaas,schoksey/networking-odl,dougwig/x-neutron-lbaas,openstack/neutron-vpnaas,schoksey/networking-odl