RFR: Update Readme with macOs specifics [v4]

Wed Mar 30 11:16:03 UTC 2022

On Tue, 29 Mar 2022 13:15:46 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.
>
> Brice Dutheil has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix typo
>   
>   Co-authored-by: Jorn Vernee <JornVernee at users.noreply.github.com>

Once you issue `/integrate` the bot will add the `sponsor` label, and then Maurizio can issue `/sponsor` to integrate it.

-------------

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