Make taurus-3.x branch deploy docs github pages
Configure the support-3.x branch to deploy docs to github.com/taurus-org/taurus-doc so that it is served in https://taurus-org.github.io/taurus-doc/v-support-3.x/
(Prior to merging, they can be seen in https://taurus-org.github.io/taurus-doc/v-deploydoc3x/ )
This is complementary to #724