Update Readme.md
Update Readme.md

Changed ipython installation command.
InsightSoftwareConsortium/SimpleITK-Notebooks,zivy/SimpleITK-Notebooks,thewtex/SimpleITK-Notebooks,zivy/SimpleITK-Notebooks,zivy/SimpleITK-Notebooks,InsightSoftwareConsortium/SimpleITK-Notebooks,thewtex/SimpleITK-Notebooks,thewtex/SimpleITK-Notebooks,InsightSoftwareConsortium/SimpleITK-Notebooks