doc: Document pg_trgm being case-insensitive by default
pg_trgm is by default operating case-insensitively but the docs didn't
mention that at all.
Author: Erik Rijkers <er@xs4all.nl>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Reported-by: marcmaiwald@googlemail.com
Discussion: https://postgr.es/m/
166064504415.652.
12724576876807446945@wrigleys.postgresql.org