doc/cephfs: edit disaster-recovery-experts (6 of x)

doc/cephfs: edit disaster-recovery-experts (6 of x)

In doc/cephfs/disaster-recovery-experts.rst, incorporate Anthony's
suggestions in

https://github.com/ceph/ceph/pull/61462#discussion_r1923917812
and
https://github.com/ceph/ceph/pull/61462#discussion_r1923920724

and reword the sentences in the section "Using an alternate metadata
pool for recovery" to be in the imperative mood, which better suits the
ordered list format that was introduced in
https://github.com/ceph/ceph/pull/61493.

Follows https://github.com/ceph/ceph/pull/61493.

https://tracker.ceph.com/issues/69557

Co-authored-by: Anthony D'Atri <anthony.datri@gmail.com>
Signed-off-by: Zac Dover <zac.dover@proton.me>