Update README to reflect changes to <Recipient> response validator that made acs-url required in #33

[camsaul]

#33 changed the way the <Recipient> response validator worked so it throws an Exception if acs-url is not set

https://github.com/metabase/saml20-clj/pull/33/files#diff-ec108a28be532b68fc3d082fae04d68aR103-R114

We need to update the README to reflect this, since it suggests otherwise.

[camsaul]

Ping @dbrrr

[dbrrr]

#42

I think the acs-url is not technically required -- it will just throw an error if the <Recipient> is present and there is no acs-url to verify against. But I changed the README to say "highly recommended :)

[dbrrr]

Ah nevermind, I reverted that change to show "required" now

Worth noting that :acs-url is passed in the request -- we could, in theory, maintain it in the StateManager for use in checking against the response.

[dbrrr]

@camsaul I think this can be closed