Update 02.01-Pose-Basics.ipynb

[NooraAz]

Since !cd creates a new shell which might be missed in next scripts, it's better to use %cd for correctly changing the directories. many students during BootCamp had problem with this, so I think it's good to add %cd notation to all notebooks.

[smith-kyle]

I'm a little late to the party, but I noticed you all aren't using a notebook review tool and wanted to invite you to review this pull request with GitNotebooks: https://gitnotebooks.com/RosettaCommons/PyRosetta.notebooks/pull/95

It lets you do things like comment on rendered markdown and code cells, so might be an easy win for your PR reviews.