suspicious wording in pg_rewind docs

Hi everyone,

While reviewing docs for [1] I came across a phrase in pg_rewind.sgml
that seems confusing:

"... The point of divergence can be found either on the target timeline,
the source timeline, or their common ancestor. In the typical failover
scenario where the target cluster was shut down soon after the
divergence, this is not a problem, but if the target cluster ran for a
long time after the divergence, the old WAL files might no longer be
present. In that case, they can be manually copied from the WAL archive
to the |pg_wal| directory, or fetched on startup by configuring
primary_conninfo
<https://www.postgresql.org/docs/12/runtime-config-replication.html#GUC-PRIMARY-CONNINFO>
or restore_command
<https://www.postgresql.org/docs/12/runtime-config-wal.html#GUC-RESTORE-COMMAND>.
"

While beginning of this paragraph talks about scanning target cluster
WALs, the "or fetched on startup" part suggests that we are applying the
source cluster WALs already, so I would simply remove it from here. To
avoid source/target confusion, we could also add another hint that it's
target WALs we are talking about.

Please consider the attached fix.

[1]
https://www.postgresql.org/message-id/a3acff50-5a0d-9a2c-b3b2-ee36168955c1%40postgrespro.ru

--
Liudmila Mantrova
Technical writer at Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company