RFR: Add jextract guide [v6]

[Jorn Vernee]

On Mon, 15 Apr 2024 13:37:51 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> doc/GUIDE.md line 226:
>> 
>>> 224: First and foremost, there is a static wrapper method that is generated that can be used to
>>> 225: call the C function (1). Besides that, there are also several accessors that return
>>> 226: additional meta-data for the method: the function's address, represented as a
>> 
>> Should we use a numbered list here too?
>
> I don't think it's possible to start a markdown list at `2`, but I will try

Looks like this doesn't work unfortunately.

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PR Review Comment: https://git.openjdk.org/jextract/pull/231#discussion_r1565850823