pgsql: doc: clarify recursion internal behavior

doc: clarify recursion internal behavior

Reported-by: Drew DeVault

Discussion: /messages/by-id/20211018091720.31299-1-sir@cmpwn.com

Backpatch-through: 10

Branch
------
REL_12_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/92cad1439f2b775211d34c7b8f42b87e02c68ace

Modified Files
--------------
doc/src/sgml/queries.sgml | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)