Add git dependency to quickstart docs
Add git dependency to quickstart docs

Without git installed, `tox -evenv -- echo 'done'` fails with a
cryptic error message. This should keep newcomers from getting
stuck on this.

Change-Id: I7cd7faa3bda905c8cfb3cfb456e3279566edf613

NaohiroTamura/ironic,SauloAislan/ironic,debayanray/ironic_backup,SauloAislan/ironic,naototty/vagrant-lxc-ironic,NaohiroTamura/ironic,openstack/ironic,faizan-barmawer/openstack_ironic,ionutbalutoiu/ironic,bacaldwell/ironic,JioCloud/ironic,varunarya10/ironic,dims/ironic,Tehsmash/ironic,naterh/ironic,openstack/ironic,froyobin/ironic,hpproliant/ironic,pshchelo/ironic,pshchelo/ironic,rdo-management/ironic,dims/ironic,ramineni/myironic,ionutbalutoiu/ironic,redhat-openstack/ironic,Tan0/ironic,bacaldwell/ironic,devananda/ironic,naototty/vagrant-lxc-ironic,supermari0/ironic,rackerlabs/ironic