Some corrections to the steps in the README

Changed chmod to allow read/write for 'other'
Removed instruction to run `./redstack start` as this is handled by
`./redstack install`
Added a reminder to save iptables rules
Added `screen -wipe` step to clean stale screen sessions

Change-Id: I72b27730cd285fb62272944dd037bdc4e907fb14
Merge "Some corrections to the steps in the README"