Doc: Pacemaker Remote: Cluster size limit 16 -> 32

Corosync is confirmed to work with up to 32 nodes as of
corosync-2.4.3-6.el7 and an unspecified early corosync-3 release (RHEL
8.1).

https://bugzilla.redhat.com/show_bug.cgi?id=1374857

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>