Unknown CMake command "python_add_library".

I followed simple git clone and tried doing `pip install ./scikit_build_example`
ended up with this error 
```
Unknown CMake command "python_add_library".
```

had to make a small tweak in CMakeLists.txt and added this line `find_package(Python COMPONENTS Interpreter Development REQUIRED)` before the line `find_package(pybind11 CONFIG REQUIRED)`
