pgsql: Doc: warn that parallel pg_restore may fail if --no-schema was u

Doc: warn that parallel pg_restore may fail if --no-schema was used.

If the archive file was made with --no-schema or related options
then it likely does not have enough dependency information to
ensure that parallel restore will choose a workable restore order.
Document this.

In passing, do some minor wordsmithing on new nearby text about
restoring from pg_dumpall archives.

Author: vaibhave postgres <postgresvaibhave(at)gmail(dot)com>
Reviewed-by: David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/CAM_eQjzTLtt1X9WKvMV6Rew0UvxT3mmhimZa9WT-vqaPjmXk-g@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/273d26b75e78a4811b0c6039c0ee38cde2341ce4

Modified Files
--------------
doc/src/sgml/ref/pg_dump.sgml | 12 ++++++++++++
doc/src/sgml/ref/pg_restore.sgml | 26 ++++++++++++++++++--------
2 files changed, 30 insertions(+), 8 deletions(-)