RFR: Add jextract guide [v5]

[Maurizio Cimadamore]

On Fri, 12 Apr 2024 19:39:26 GMT, Nir Lisker <nlisker at openjdk.org> wrote:

> Did you leave out "Bitfields" on purpose?

Jextract does not support bitfields (due to deficiencies in the libclang API). That's why there's no section for them :-)

> doc/GUIDE.md line 29:
> 
>> 27: library called `mylib` stored at `/path/to/mylib` that has a directory `/path/to/mylib/include`
>> 28: where the header files of that library are stored. And let's say that we have a shell open
>> 29: in the root directory of the Java project we're working on, which has an `src` source
> 
> "a `src`" probably.

I believe this was discussed here:
https://github.com/openjdk/jextract/pull/231#discussion_r1559141069

> doc/GUIDE.md line 348:
> 
>> 346: 
>> 347: For working with arrays of structs, we can use the `allocateArray` method which accepts an
>> 348: additional element count, indicating the length of the array:
> 
> Comma before "which" instead of after "count".

I find the way it's currently written fine (and better than the suggested one)

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PR Comment: https://git.openjdk.org/jextract/pull/231#issuecomment-2052541652
PR Review Comment: https://git.openjdk.org/jextract/pull/231#discussion_r1563207432
PR Review Comment: https://git.openjdk.org/jextract/pull/231#discussion_r1563205742