docker instructions need updating

[shimwell]

Reported by a user that the instructions don't quite work.

Step 3
sudo docker run -p 8888:8888 ukaea/paramak /bin/bash -c "jupyter notebook --notebook-dir=/opt/notebooks --ip='*' --port=8888 --no-browser --allow-root"

doesn’t seem to work as it cannot find the directory /opt/notebooks

removing --notebook-dir=/opt/notebooks works and provides a couple of URLs

Opening one in the browser and looking in /opt there is indeed no folder called notebooks, I am struggling to find any notebooks anywhere

[shimwell]

this is being worked on in #756