With the separation of Zuul and OpenDev from OpenStack and the
dissolution of the Infrastructure project team, the /infra/
documents are increasingly focused on things maintained by the
Testing and Collaboration Tools SIG. Rename and describe it in the
main docs index accordingly.
Change-Id: I3dfede540bb6434c60698e1af3c4fd0a8cde3712
Depends-On: I885561912cd719afdfc02f382dcf36b08540ec00