Thread: pgsql: Doc: improve documentation about ts_headline() function.

Doc: improve documentation about ts_headline() function.

Now that I've had my nose in that code, I thought the docs about
it left something to be desired.

Branch
------
REL9_6_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/12c2b7a37072d991aa15ca453f0cfcb3620d03f6

Modified Files
--------------
doc/src/sgml/textsearch.sgml | 105 ++++++++++++++++++++++++-------------------
1 file changed, 58 insertions(+), 47 deletions(-)