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

[Johan Vos]

On Tue, 14 Sep 2021 12:11:00 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> CONTRIBUTING.md line 14:
>> 
>>> 12: ```
>>> 13: 
>>> 14: where `LONG-COMMIT-HASH` is the long (40 char) commit hash of the fix as found in the main jfx repo. The Skara tooling will then note that it is a backport, and replace the title with the correct issue title.
>> 
>> Should the next parts of the process be explained as well (e.g. optional review if no clean patch, merging?)
>
> 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

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