chore(README): Format local/system parameters as table

[guicamest]

Description of changes:

This PR formats local and system parameters in the README as a table, in order to improve reading

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[guicamest]

I think it can even be written as

parameter	type	description
aws.region	local/system	specifies the default region for API calls
..	..
s3.spi.endpoint	local	the endpoint to use to access the bucket; this is extracted from the uri by the S3X provider
..	..

Might be easier to maintain / read since there is less text. What do you think?

[markjschreiber]

Thanks!