docs: Provide new Readme for MacOS

Short README for usage of ct-ng under MacOS.
Remove obsolete MacOS-X.txt

yann.morin.1998@anciens.enib.fr:
Make it 80-columns clean, plus a few fixes

 reporter_name="Thomas Petazzoni"

 reporter_url="http://www.free-electrons.com/"

 reporter_comment="Very basic testing only"