RFR: Add guide section about platform-dependent nature of jextract

[Maurizio Cimadamore]

On Wed, 17 Apr 2024 21:06:04 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> The current guide is lacking a discussion about the platform dependent nature of jextract, leaving users to wonder if and when the bindings generated by jextract can be used on different platforms.
>> 
>> This PR adds a couple of paragraphs to the guide to explain this.
>> 
>> Note: I've also fixed a typo in the README.
>
> doc/GUIDE.md line 88:
> 
>> 86: [Using The Code Generated By Jextract section](#using-the-code-generated-by-jextract)).
>> 87: 
>> 88: Generally speaking, the code that jextract generates is dependent on the platform on which
> 
> Suggestion:
> 
> Generally speaking, the bindings generated by jextract depend on the platform on which

The above is to streamline things a bit (optional)

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PR Review Comment: https://git.openjdk.org/jextract/pull/237#discussion_r1569555605