Update readme.md

A docker container for running Synology's Virtual DSM.

## Prerequisites

In order to use the container, you need two images called `boot.img` and `system.img` from Synology containing the Virtual DSM 7 OS. 

Place them in the `/home/user/images` folder. A third empty image, called `data.img` will be automaticly generated with a size of 16GB. If you need more space for your DSM instance, you can manually generate a larger file by running `truncate -s 100G data.img` on your host OS.

## Using the container

Via `docker run`:

```bash

$ docker run --rm -it \

    -p 5000:5000 \

    --cap-add NET_ADMIN \

    --cap-add SYS_ADMIN \

    --device=/dev/kvm:/dev/kvm \

    --device=/dev/fuse:/dev/fuse \

    --device=/dev/net/tun:/dev/net/tun \    

    --cap-add NET_ADMIN \

    -p 5000:5000 -p 5001:5001 \

    -v /home/user/images:/images \

    kroese/virtual-dsm:latest

```

        image: kroese/virtual-dsm:latest

        cap_add:

            - NET_ADMIN

            - SYS_ADMIN

        devices:

            - /dev/kvm

            - /dev/fuse

            - /dev/net/tun

        ports:

            - 5000:5000

            - 5001:5001

        volumes:

            - /home/user/images:/images

        restart: always