ENH: Added R installing instructions for Ubuntu.
ENH: Added R installing instructions for Ubuntu.

Quick list of the packagages that must be installed in Ubuntu in order to use
the R wrapping.

richardbeare/SimpleITK,InsightSoftwareConsortium/SimpleITK,hendradarwin/SimpleITK,hendradarwin/SimpleITK,InsightSoftwareConsortium/SimpleITK,blowekamp/SimpleITK,richardbeare/SimpleITK,SimpleITK/SimpleITK,InsightSoftwareConsortium/SimpleITK,SimpleITK/SimpleITK,hendradarwin/SimpleITK,richardbeare/SimpleITK,kaspermarstal/SimpleElastix,richardbeare/SimpleITK,blowekamp/SimpleITK,hendradarwin/SimpleITK,richardbeare/SimpleITK,InsightSoftwareConsortium/SimpleITK,blowekamp/SimpleITK,blowekamp/SimpleITK,blowekamp/SimpleITK,SimpleITK/SimpleITK,kaspermarstal/SimpleElastix,hendradarwin/SimpleITK,hendradarwin/SimpleITK,hendradarwin/SimpleITK,SimpleITK/SimpleITK,kaspermarstal/SimpleElastix,InsightSoftwareConsortium/SimpleITK,blowekamp/SimpleITK,kaspermarstal/SimpleElastix,hendradarwin/SimpleITK,richardbeare/SimpleITK,SimpleITK/SimpleITK,richardbeare/SimpleITK,InsightSoftwareConsortium/SimpleITK,blowekamp/SimpleITK,blowekamp/SimpleITK,InsightSoftwareConsortium/SimpleITK,kaspermarstal/SimpleElastix,SimpleITK/SimpleITK,kaspermarstal/SimpleElastix,kaspermarstal/SimpleElastix,SimpleITK/SimpleITK,richardbeare/SimpleITK,InsightSoftwareConsortium/SimpleITK,SimpleITK/SimpleITK