Building shortcuts

[sverhoeven]

The guide uses shortcuts for building/deployment you would not take if you made a real web application/service.

1. You don't compile pybind11 yourself, but let a build system like setup.py or cmake do it, see https://pybind11.readthedocs.io/en/master/compiling.html
2. You don't call emcc yourself, but let a build system like emconfigure, emmake or package.json do it, see https://emscripten.org/docs/compiling/Building-Projects.html#integrating-with-a-build-system
3. If WebAssembly module is re-usable you publish it to npmjs