Docs: Cross ref local tests on contribution guide
Docs: Cross ref local tests on contribution guide

Cross reference the development and testing scripts,
tox builds, etc, in the Contributor Guidelines.

As a new contributor to openstack-ansible I was focused
on the Contributor Guidelines and did not find the list of tox
targets hidden under the "Included Scripts" page.

Change-Id: I3332722a517e498c8a19605df998bb739a86991d

robb-romans/openstack-ansible,Logan2211/openstack-ansible,BjoernT/os-ansible-deployment,stackforge/os-ansible-deployment,openstack/openstack-ansible,weezer/openstack-ansible,cfarquhar/openstack-ansible,cloudnull/os-ansible-deployment,BjoernT/openstack-ansible,BjoernT/openstack-ansible,yanyao/openstack-ansible,BjoernT/os-ansible-deployment,major/openstack-ansible,major/os-ansible-deployment,weezer/openstack-ansible,openstack/openstack-ansible,BjoernT/os-ansible-deployment,bunchc/openstack-ansible,os-cloud/os-ansible-deployment,mancdaz/openstack-ansible,major/os-ansible-deployment,cfarquhar/openstack-ansible,major/openstack-ansible,cloudnull/os-ansible-deployment,stackforge/os-ansible-deployment,mancdaz/openstack-ansible,bunchc/openstack-ansible,os-cloud/os-ansible-deployment,yanyao/openstack-ansible,yanyao/newton,robb-romans/openstack-ansible,Logan2211/openstack-ansible,yanyao/newton