README instructions wrong, can't build anymore

[kunitoki]

The readme mentions a hypothetical build_rive.sh script which is not found in the rive-cpp submodule, the only script available there is build.sh which needs to be executed from the rive-cpp folder (so adding rive-cpp/build on the PATH has no use).

What are the instructions to build the rive renderer ?

[ScatteredRay]

@kunitoki be careful about the PATH, as it's rive-cpp/build not just rive-cpp The file is still there for me: https://github.com/rive-app/rive-cpp/blob/master/build/build_rive.sh