Broken notebook symlinks

[rafa-guedes]

There are broken notebooks symlinks in the docs, since the notebooks are no longer in the core rompy repo. @tomdurrant where are the docs being built now? Can we delete these?

[tomdurrant]

My current plan is to checkout the notebooks repo as part of the docs build. However how docs work across split repos in general needs some thought. This will be looked at as part of the next piece of work