Update README.md

adding some additional information to the readme file

README.md

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 # docker_hddfancontrol
 simple Docker image for hddfancontrol by desbma
+https://github.com/desbma/hddfancontrol
+
+This is a docker image which includes the following programs to run **hddfancontrol** by desbma.
+- smartmontools - needed for the new --smartctl option, which uses smartmontolls instead of hdparm to spindown drives
+- hdparm - old way of spinning down drives
+- hddtemp - to get hddtemps
+- fancontrol - to control PWM fan speed
+
+
+### Current prerequisite
+Since it is not good measure to load kernel modules inside docker you need to do the following before usign this container
+- Installing the `lm-sensors` package for your distribution
+- run `sensors-detect` with standard configuration
+- load the detected kernel modules by adding them to /etc/modules (This can be done automatically in the step above)
+
+
+### Docker compose
+- The environment variable ARGS is used to give the needed paramters to hddfancontrol
+- currently privbiliged mode is used, since I didnt find an easy way to bind the sysfs hwmon instances 
+```
+version: "2"
+services:
+  hddfancontrol:
+    image: fred92/hddfancontrol:latest
+    restart: unless-stopped
+    privileged: true
+    environment:
+      - ARGS=-d /dev/sdb /dev/sdc /dev/sdd -p /sys/class/hwmon/hwmon2/pwm1 /sys/class/hwmon/hwmon2/pwm2 --pwm-start-value 70 80 --pwm-stop-value 20 30 --min-fan-speed-prct 0 -i 60 --spin-down-time 600 -l /var/log/hddfancontrol.log --smartctl
+```
+
+### ToDo
+- [ ] Split the $ARGS environment variable into the individual configuration paramters
+- [ ] Find a way to get rid of the priviliged mode and use the devices directly
+- [ ] incoperate lm-sensors into the container including the kernel modules
+