The QuickstartGuide_softbody.pdf contains the following information.
But ObiSoftbody.unitypackage is not in my project.
Quote:1.- Include the Obi package in your project. Right click in the project window, "Import
Package" → "Custom Package", then select ObiSoftbody.unitypackage.
But ObiSoftbody.unitypackage is not in my project.