Update documentation
Update documentation

A couple missing steps in the installation section.

lukejharmon/tangelohub,adsorensen/flow,adsorensen/flow,lukejharmon/tangelohub,Kitware/flow,Kitware/tangelohub,adsorensen/flow,Kitware/tangelohub,Kitware/tangelohub,Kitware/flow,lukejharmon/tangelohub,adsorensen/flow,Kitware/flow,adsorensen/flow,Kitware/flow