You don't have to run the rakefile task until you are planning to do development on the measures (i.e., make changes to them). You can just download/clone the measures and run use them as is.

That said, the warning about those 2 measures is safe to ignore. Currently these 2 measures (to model PV and interact with the FloorspaceJS tool) are not available, hence the warnings. (The PV measure should be available in a month or so, we're just waiting on the PVWatts model to be available in an OpenStudio release.)