Update readme to reflect moved sample files

[joellabes]

Sample files now live in the same s3 bucket as the classic jaffle shop (but in a subdirectory), so that the sharing rules are consistent. We were seeing that the old bucket couldn't be accessed from Snowflake for some reason.

I've also added:

• a direct download link for each file, so that people can alternatively download the file and then reupload it into their warehouse of choice
• the schema for each table to make it easier to manually write create table statements

I've validated that all files can be successfully copied into Snowflake and accessed from DuckDB.

I recommend using the visual diff:

[joellabes]

Postgres is failing but is not related to this change :(