Update README.md

[austinsonger]

No description provided.

[netbix]

I propose this change:
in docker scanner openvas is missing persistent folder association with ssh data
/ var / lib / gvm

docker run --detach --volume ./storage/openvas-plugins:/var/lib/openvas/plugins ./storage/gvm:/var/lib/gvm --env MASTER_ADDRESS={IP or Hostname of GVM container} --env MASTER_PORT=2222 --name scanner securecompliance/openvas

[austinsonger]

@netbix You propose this change to documentation?