Update ERC-5573: require single recap in resources

[chris13524]

"a Recap URI MUST occupy the final entry of the SIWE resource list" is somewhat ambiguous as to if there can be more (implied ignored) urn:recap URIs elsewhere in the resource list. Making this more explicit that there must be a single urn:recap URI.

Also adjust spacing and indent to be consistent with elsewhere in the spec & fix some caps typos.

[eip-review-bot]

File ERCS/erc-5573.md

Requires 1 more reviewers from @awoie, @chunningham, @clehner, @cobward, @skgbafa, @wyc

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[chris13524]

I still think this is worth addressing/merging