doc/rados: edit pools.rst (2 of x)

doc/rados: edit pools.rst (2 of x)

Edit doc/operations/rados/pools.rst.

There remains confusion in this part of the document regarding pg_num
and pgp_num. pg_num and pgp_num are not explained with sufficient
clarity. A future commit will clear up this confusion. There is also
some potential confusion between on the one hand the strings "pg-num"
and "pgp-num" and on the other hand "pg_num" and "pgp_num". The strings
with the hyphens are used in dummy commands, and the strings with the
underscores are used as key names. I think it possible that this could
confuse a reader, but I am open to discussion on the matter.

https://tracker.ceph.com/issues/58485

Co-authored-by: Anthony D'Atri <anthony.datri@gmail.com>
Signed-off-by: Zac Dover <zac.dover@proton.me>
(cherry picked from commit fe9a4d2567dbf0ebfc633ed2a0ceb7d86c70f525)