[Feature request] Support for embedding binaries a la pyinstaller's --add-binary

We currently distribute an app built using pyinstaller, which embeds a C++ executable using the `--add-binary` flag ([link to the more relevant `--add-data` docs](https://pyinstaller.org/en/stable/usage.html#cmdoption-add-data)). I couldn't see an analogous flag for PyApp, is there any way to add more data to the built app? I think we could move off pyinstaller if we had this, everything else seems to be working fine (with shockingly little effort, great work!)