RFR: Add jextract guide [v5]

Mon Apr 15 13:46:10 UTC 2024

On Mon, 15 Apr 2024 13:19:45 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> But we can't call the c function directly. Are there more java bindings that jextract generates?
>
> Sorry, the example assumes that that the `call_me_back` function is also defined in the header file that jextract extracted, so a Java method would be generated for it.

I would mentioned that. After all, this tool is meant to save Java developers from knowing the intricacies of the native language.

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PR Review Comment: https://git.openjdk.org/jextract/pull/231#discussion_r1565817933