add types to index storage params on doc

Hi,

The current manual on CREATE TABLE[1] describes storage
parameters with their types.
But manual on CREATE INDEX[2] describes storage parameters
WITHOUT their types.

I think it'll be better to add types to storage parameters
on CREATE INDEX for the consistency.

Attached a patch.
Any thought?

[1]https://www.postgresql.org/docs/devel/sql-createtable.html#SQL-CREATETABLE-STORAGE-PARAMETERS
[2]https://www.postgresql.org/docs/devel/sql-createindex.html#SQL-CREAT`INDEX-STORAGE-PARAMETERS

Regards,
--
Torikoshi Atsushi