doc/cephadm: improve front matter

- I fixed a sentence that was missing a verb.
- I linked to the Ceph-specific Rook instructions.
- I removed the word "GitHub", because after adding the
  Rook instructions it made the sentence false.

Signed-off-by: Zac Dover <zac.dover@gmail.com>
(cherry picked from commit 608b1bdd42f1da75b43584fa45586575ccef0290)

Merge pull request #48594 from zdover23/wip-doc-2022-10-23-backport-48593-to-quincy

quincy: doc/cephadm: update install.rst

Reviewed-by: Cole Mitchell <cole.mitchell@gmail.com>

doc/cephadm: update install.rst

This commit addresses https://github.com/ceph/ceph/pull/43250,
which has remained unmerged for thirteen months. The issues
raised in that PR are addressed here.

This commit contributes to the simplification of the procedure
that explains how to install cephadm. More remains to be done
on this page, but the old PR had to be dealt with first.

Signed-off-by: Zac Dover <zac.dover@gmail.com>
(cherry picked from commit c8f01d3a32b889a0f3b68f619bfed36f6579c28b)

Merge pull request #48268 from vshankar/tr-57193

quincy: fsmap: switch to using iterator based loop

Reviewed-by: Milind Changire <mchangir@redhat.com>