I don't understand why they haven't put this into a Linux package? If you want it to get widely adopted, surely you should make it easier for software to add dependencies on your image type. For example one of my projects currently depends on libjpeg and libjpeg-dev for building.
And it should also be available from both Homebrew and MacPorts.
To convert a .webp image, use dwebp foo.webp -o foo.png