improve zipfian documentation about performance

When Who What
2019-04-01 21:37:54 Tom Lane (tgl) Closed in commitfest 2019-03 with status: Committed
2019-04-01 21:02:47 Tom Lane (tgl) Added tgl as committer
2019-03-13 09:56:40 Georgios Kokolatos (gkokolatos) Posted review with messageid <155247100007.16480.7209755354754262427.pgcf@coridan.postgresql.org>
2019-03-13 09:56:40 Georgios Kokolatos (gkokolatos) New status: Ready for Committer
2019-03-13 08:55:10 Georgios Kokolatos (gkokolatos) Posted review with messageid <155246731010.16480.15850913449923768119.pgcf@coridan.postgresql.org>
2019-03-13 08:50:21 Georgios Kokolatos (gkokolatos) Added gkokolatos as reviewer
2019-02-28 11:23:36 Fabien Coelho (calvin) Changed targetversion to stable
2019-02-28 11:23:36 Fabien Coelho (calvin) Changed authors to Fabien Coelho (calvin)
2019-02-28 11:22:21 Fabien Coelho (calvin) Attached mail thread b5e172e9-ad22-48a3-86a3-589afa20e8f7@2ndquadrant.com
2019-02-28 11:22:21 Fabien Coelho (calvin) Created patch record