[jfx23u] Integrated: 8304008: Update README.md and CONTRIBUTING.md for jfx update repos

[Johan Vos]

On Fri, 12 Jul 2024 14:41:27 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

> This is a copy of the jfx22u README and CONTRIBUTING docs, changing 22 to 23, with one additional change to add the word "Updates" after "23" in one place where it was missing (the current wording could mislead developers into thinking that JavaFX 23 fixes should be done here).
> 
> I'll take this out of Draft once PR #1 is integrated (that PR _must_ be integrated ahead of anything else and before I announce that the repo is open for pull requests).

Marked as reviewed by jvos (Reviewer).

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PR Review: https://git.openjdk.org/jfx23u/pull/2#pullrequestreview-2185642838