docs: Fix format of CREATE FOREIGN TABLE example in postgres_fdw

Hi,

while reading https://www.postgresql.org/docs/devel/postgres-fdw.html  I've noticed that there is a single bracket on one line of the CREATE FOREIGN TABLE example.

Browsing through other docs (e,g. https://www.postgresql.org/docs/devel/sql-createtable.html ) there doesn't seem to be a rule for that but if there is a single bracket (e.g. CREATE TABLE distributors), the options that follow usually start at position one and are not indented (or they follow directly after the bracket).

The examples in file_fdw (https://www.postgresql.org/docs/devel/file-fdw.html) follow a mix of options which directly follow the bracket and on a new line.

Attached a small patch which makes it looking a bit better, at least in my opinion.

Regards
Daniel