pgsql: doc: explain pgstatindex fragmentation

doc: explain pgstatindex fragmentation

It was quite hard to guess what leaf_fragmentation meant without looking
at pgstattuple's code.  This patch aims to give to the user a better
idea of what it means.

Author: Frédéric Yhuel <frederic.yhuel@dalibo.com>
Author: Laurenz Albe <laurenz.albe@cybertec.at>
Reviewed-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Reviewed-by: Benoit Lobréau <benoit.lobreau@dalibo.com>
Discussion: https://postgr.es/m/bf110561-f774-4957-a890-bb6fab6804e0%40dalibo.com
Discussion: https://postgr.es/m/4c5dee3a-8381-4e0f-b882-d1bd950e8972@dalibo.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/960135114629bc89da0dd1d839541098c7e6401a

Modified Files
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doc/src/sgml/pgstattuple.sgml | 9 +++++++++
1 file changed, 9 insertions(+)