Doc: fix incorrect EXPLAIN ANALYZE output for bloom indexes

Doc: fix incorrect EXPLAIN ANALYZE output for bloom indexes

It looks like the example case was once modified to increase the number
of rows but the EXPLAIN ANALYZE output wasn't updated to reflect that.

Also adjust the text which discusses the index sizes.  With the example
table size, the bloom index isn't quite 8 times more space efficient
than the btree indexes.

Discussion: https://postgr.es/m/CAApHDvovx8kQ0=HTt85gFDAwmTJHpCgiSvRmQZ_6u_g-vQYM_w@mail.gmail.com
Backpatch-through: 13, all supported versions