RFR: Add jextract guide [v5]

Tue Apr 16 00:14:02 UTC 2024

On Mon, 15 Apr 2024 13:39:47 GMT, Nir Lisker <nlisker at openjdk.org> wrote:

>> 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.

Was this resolved? I don't see a clarification (maybe I'm missing it).

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PR Review Comment: https://git.openjdk.org/jextract/pull/231#discussion_r1566554742