doc: add section for strategic initiatives

Add reference to strategic initiatives on core README.md
in order to ensure broarder visibility.

PR-URL: https://github.com/nodejs/node/pull/17104


Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>