Broken iota private network instructions

[daria305]

Instructions from README don't work. As we have now separated directories setups/... and `dev-tools/.., and previously all was in one dir.

Now we need to jump between dev-tools and docker dirs to build images and go back to run the scripts, as iota/docker/iota-node/build.sh scripts wont work from outside its own dir.

[nmrshll]

I've noticed the same problems and fixed it as part of testing #4666 (the private network is needed to launch the local grafana)
This should be fixed once I merge #4666