RFR: Update Readme with macOs specifics [v2]

[Maurizio Cimadamore]

On Tue, 29 Mar 2022 10:14:59 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 review comments

README.md line 15:

> 13: ```
> 14: 
> 15: <details><summary>Using a local installation of LLVM</summary>

Can we do this in bold, and also perhaps use the quote mechanism - e.g.

> <details><summary><b>Using a local installation of LLVM</b></summary>Some text</summary>

README.md line 28:

> 26: </details>
> 27: 
> 28: After building, there should be a new `jextract` folder under `build` (the contents and the name of this folder might vary slightly depending on the platform, e.g. on macOs the folder is `jextract.app`) :

Do you think it is still necessary to provide specific details about macOs here (and below) ?

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