Minor bugfixes for the README

[joakimlindblad]

Under: https://github.com/eryl/aida-gnn-workshop-code/#installing-dependencies-for-local-use

1. Lacking cd aida-gnn-workshop-code/ somewhere before conda env create -f environment.yml --solver=libmamba

2. Should no it be jupyter notebook (without 's') or did I misunderstand your intention?

(3. You might mention somewhere that conda+env setup takes ca 20GB disk.)

Thanks for the great tutorial!