This patch fixes the partitioning synopsis in the Parameters section in
the CREATE FOREIGN TABLE documentation.  Follow-up for commit ce21a36cf.

Back-patch to v11 where default partition was introduced.

Reviewed by Amit Langote and Robert Haas.

Discussion: https://postgr.es/m/CAPmGK17U5jEqVZuo3r38wB0VFWomEtJCBGn_h92HQzQ2sP-49Q%40mail.gmail.com