Revise Storage section, considerations for multiple storages

[VirginiaBalseiro]

Following discussion on: https://github.com/solid/webid-profile/blob/main/meetings/2022-10-25.md and part of a revision of the Storage section.

It would be useful to list use cases for multiple storages, and how a client could handle this case. This is in line with a "best practices" document, but we still should revise section on storage and discuss this scenario.

Related: #53 #55