[jfx17u] RFR: 8273280: Update README.md and CONTRIBUTING.md for jfx17u

[Kevin Rushforth]

On Tue, 14 Sep 2021 12:25:55 GMT, Johan Vos <jvos at openjdk.org> wrote:

>> Good idea, but I'd prefer to do that as a follow-on fix; that change could then be backported to jfx11u (as a clean backport).
>
> makes sense

I filed https://bugs.openjdk.java.net/browse/JDK-8273732 as a follow-up.

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PR: https://git.openjdk.java.net/jfx17u/pull/1