doc: Minor wordsmithing to COPY docs
Perform some minor wordsmithing on two sentences in the COPY documentation
to make them clearer.
While there, also ensure to wrap a few occurrences of CSV in <literal>
which were missing this.
Reported-by: Eric Mutta <eric.mutta@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/
166104548566.654.
11680826843612576896@wrigleys.postgresql.org