hoauth2-2.15.0: README.md

Haskell binding for

-   [The OAuth 2.0 Authorization Framework](https://datatracker.ietf.org/doc/html/rfc6749)
    -   If the Identity Provider also implements [OIDC
        spec](https://openid.net/specs/openid-connect-core-1_0.html), ID
        Token will also be present in token response (see
        `OAuth2Token`).
-   [JWT Profile for OAuth2 Client Authentication and Authorization
    Grants](https://www.rfc-editor.org/rfc/rfc7523.html)
-   [The OAuth 2.0 Authorization Framework: Bearer Token
    Usage](https://www.rfc-editor.org/rfc/rfc6750)