doc/start: add testing support information
This PR adds information about support for testing,
and information about which distros the Ceph project
builds packages for.
This is one in a series of PRs including the following:
https://github.com/ceph/ceph/pull/45385
https://github.com/ceph/ceph/pull/45764
This PR specifically includes the information that Ernesto
Puerta collected here:
https://github.com/ceph/ceph/pull/45385#pullrequestreview-
911766656
Signed-off-by: Zac Dover <zac.dover@gmail.com>
(cherry picked from commit
0364f3afcccc85d190237b0a74b4deeefa4738f3)