pgsql: doc: Add example file for COPY

doc: Add example file for COPY

The paragraph for introducing INSERT and COPY discussed how a file
could be used for bulk loading with COPY, without actually showing
what the file would look like. This adds a programlisting for the
file contents.

Backpatch to all supported branches since this example has lacked
the file contents since PostgreSQL 7.2.

Author: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Fujii Masao <masao.fujii@oss.nttdata.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: /messages/by-id/158017814191.19852.15019251381150731439@wrigleys.postgresql.org
Backpatch-through: 13

Branch
------
REL_18_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/409c63f9f634c1d9aa5a4afb17f54056b3de7c88

Modified Files
--------------
doc/src/sgml/query.sgml | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)