pgsql: relnotes: PG 12, mention change in libpq parameter parsing

relnotes: PG 12, mention change in libpq parameter parsing

Reported-by: emorley@heroku.com

Diagnosed-by: Michael Paquier

Discussion: https://postgr.es/m/157123155668.25311.9369950798665566339@wrigleys.postgresql.org

Author: Michael Paquier

Reviewed-by: me

Backpatch-through: 12 only

Branch
------
REL_12_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/9de37ea65188167b0dc0acb3ce25f031c6cb4d79

Modified Files
--------------
doc/src/sgml/release-12.sgml | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)