pgsql: doc: improve NLS instruction wording

doc: improve NLS instruction wording

Reported-by: "Tang, Haiying"

Discussion: /messages/by-id/bbbccf7a3c2d436e85d45869d612fd6b@G08CNEXMBPEKD05.g08.fujitsu.local

Author: "Tang, Haiying"

Backpatch-through: 9.5

Branch
------
REL9_6_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/72c2187eb7df51f73cdbc034f1ddf31f01611155

Modified Files
--------------
doc/src/sgml/nls.sgml | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)