Update platform notes to build Postgres on macos

Hi,

I just built postgresql on macos sonoma (v14) and I had to install the following packages:

• * icu - https://ports.macports.org/port/icu/
• * pkg - https://ports.macports.org/port/pkgconfig/

I don't see anything related to this on https://www.postgresql.org/docs/devel/installation-platform-notes.html

Did I miss something ? Should we add a note?

best,
Saïd