Add volume option to example command

Author: hectorm

README.md

@@ -12,6 +12,7 @@ docker run --detach \
   --publish 127.0.0.1:3389:3389/tcp \
   --publish 127.0.0.1:5900:5900/tcp \
   --publish 127.0.0.1:6080:6080/tcp \
+  --mount type=volume,src=qemu-win2000-disk,dst=/var/lib/qemu/disk/ \
   docker.io/hectorm/qemu-win2000:latest
 ```