Fix README
Fix README

Given that the FileWatchSensor is disabled by default
(check the content of /opt/stackstorm/packs/linux/sensors/file_watch_sensor.yaml
file in the container), doing a st2ctl reload after enabling this sensor
will disable it. So, we have to enable the sensor after the reload.

shusugmt/st2-docker,shusugmt/st2-docker