RFR: Update Readme with macOs specifics

[Brice Dutheil]

On Mon, 28 Mar 2022 20:25:46 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> I felt the same and wondered if a different file was needed, but the details block looks good for me.
>> 
>> Regarding Linux (or else) I felt this was an opportunity to document these LLVM installs as well. And may improve usability.
>> 
>> After reading your comment I think that if the build should prefer an actual download of LLVM it might be better to write a gradle task that performs the download and extraction. It should be quite ready and it might improve the deterministic aspect as the build.
>
>> After reading your comment I think that if the build should prefer an actual download of LLVM it might be better to write a gradle task that performs the download and extraction. It should be quite ready and it might improve the deterministic aspect as the build.
> 
> This is something we are considering, for both the JDK and libclang.

Thank you @mcimadamore @JornVernee

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PR: https://git.openjdk.java.net/jextract/pull/10