pgsql: doc: document problems with using xreflabel in XML docs

doc: document problems with using xreflabel in XML docs

Reported-by: Peter Eisentraut

Discussion: /messages/by-id/8315c0ca-7758-8823-fcb6-f37f9413e6b6@2ndquadrant.com

Backpatch-through: master

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/59fa7eb60364b8e71fe0f515d6ad87c274af839b

Modified Files
--------------
doc/src/sgml/README.links | 4 ++++
1 file changed, 4 insertions(+)