Integrated: Update Readme with macOs specifics

[Brice Dutheil]

On Mon, 28 Mar 2022 16:32:42 GMT, Brice Dutheil <duke at openjdk.java.net> wrote:

> The macOs libclang location as well as build output differ enough to warrant specific information. In particular the use of the XCode based path to find the libclang is not an easy find. The output also makes use of jpackage with `app-image` type, but the macOs _.app_ layout different enough on macOs.

This pull request has now been integrated.

Changeset: 07d81c73
Author:    Brice Dutheil <brice.dutheil at gmail.com>
Committer: Maurizio Cimadamore <mcimadamore at openjdk.org>
URL:       https://git.openjdk.java.net/jextract/commit/07d81c73208d53319920f7ffd1fa90d0b04de466
Stats:     19 lines in 1 file changed: 16 ins; 0 del; 3 mod

Update Readme with macOs specifics

Reviewed-by: jvernee, mcimadamore

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