[DOCS] effective_io_concurrency option in ALTER TABLESPACE

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Page: https://www.postgresql.org/docs/9.6/static/sql-altertablespace.html
Description:

This page:
https://www.postgresql.org/docs/9.6/static/runtime-config-resource.html

Tell about effective_io_concurrency could be changed for a specific
tablespace and refer to this page:
https://www.postgresql.org/docs/9.6/static/sql-altertablespace.html
Who said "Currently, the only available parameters are seq_page_cost and
random_page_cost." and refer to them.

Option "effective_io_concurrency" is missing as I tried the following
command and it worked:
alter tablespace emet_temp set (effective_io_concurrency=50);

Cheers