Adding info about xdebug mac vs linux

docker/app/enabled-xdebug.ini

 zend_extension=xdebug.so
+; MacOS with DockerForMac:
+;    remote_connect_back has to be on 0
+;    remote_host and remote_port uncommented
+; Linux:
+;    remote_connect_back has to be on 1
+;    remote_host and remote_port commented
 xdebug.remote_enable=1
-xdebug.remote_connect_back=1
+xdebug.remote_connect_back=0
+xdebug.remote_host=docker.for.mac.localhost
+xdebug.remote_port=9000