doc: Added the crisp getting started guide to index.rst

doc: Added the crisp getting started guide to index.rst

This commit adds the 3-node getting started procedure to the
doc/index.rst file and represents the first large action taken
toward making the Ceph documentation more user-friendly and more
comprehensible to readers who have never used Ceph before.

Signed-off-by: Zac Dover <zac.dover@gmail.com>
Added jdurgin's notes.

Signed-off-by: Zac Dover <zac.dover@gmail.com>
Removed "podman" per jdurgin's direction.

Signed-off-by: Zac Dover <zac.dover@gmail.com>
changed a path from sdb1 to /by-id/[long string]w

Signed-off-by: Zac Dover <zac.dover@gmail.com>
changed the command for copying the keyring and the conf file, per jdurgin

Signed-off-by: Zac Dover <zac.dover@gmail.com>