Effective IO Concurrency

Hi!

In PostgreSQL 13, the way of using effective_io_concurrency has changed. Until v12, I used 200 for this value (using SSD drives). Using the new formula described in https://www.postgresql.org/docs/13/release-13.html gives me 1176. However, in the documentation https://www.postgresql.org/docs/13/runtime-config-resource.html#GUC-EFFECTIVE-IO-CONCURRENCY it says that the maximum value allowed is 1000.