PG-1832 Document the archive and restore commands cont

[Andriciuc]

Continued from #523

[AndersAstrand]

We have changed how these two commands works since this was written, here are the usage instructions for each:

pg_tde_archive_decrypt

pg_tde_archive_decrypt wraps an archive command to give the command unencrypted WAL.

Usage:
  pg_tde_archive_decrypt [OPTION]
  pg_tde_archive_decrypt DEST-NAME SOURCE-PATH ARCHIVE-COMMAND

Options:
  -V, --version   output version information, then exit
  -?, --help      show this help, then exit
  DEST-NAME       name of the WAL file to send to archive
  SOURCE-PATH     path of the source WAL segment to decrypt
  ARCHIVE-COMMAND archive command to wrap, %p will be replaced with the
                  absolute path of the decrypted WAL segment, %f with the name

Note that any %f or %p parameter in ARCHIVE-COMMAND will have to be escaped
as %%f or %%p respectively if used as archive_command in postgresql.conf.
e.g.
  archive_command='pg_tde_archive_decrypt %f %p "cp %%p /mnt/server/archivedir/%%f"'
or
  archive_command='pg_tde_archive_decrypt %f %p "pgbackrest --stanza=your_stanza archive-push %%p"'

pg_tde_restore_encrypt

pg_tde_restore_encrypt wraps a restore command to encrypt its returned WAL.

Usage:
  pg_tde_restore_encrypt [OPTION]
  pg_tde_restore_encrypt SOURCE-NAME DEST-PATH RESTORE-COMMAND

Options:
  -V, --version   output version information, then exit
  -?, --help      show this help, then exit
  SOURCE-NAME     name of the WAL file to retrieve from archive
  DEST-PATH       path where the encrypted WAL segment should be written
  RESTORE-COMMAND restore command to wrap, %p will be replaced with the path
                  where it should write the unencrypted WAL segment, %f with
                  the WAL segment's name

Note that any %f or %p parameter in RESTORE-COMMAND will have to be escaped
as %%f or %%p respectively if used as restore_command in postgresql.conf.
e.g.
  restore_command='pg_tde_restore_encrypt %f %p "cp /mnt/server/archivedir/%%f %%p"'
or
  restore_command='pg_tde_restore_encrypt %f %p "pgbackrest --stanza=your_stanza archive-get %%f \"%%p\""'