Run cmake-init and setup flake.nix and default.nix

BUILDING.md

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+# Building with CMake
+
+## Build
+
+This project doesn't require any special command-line flags to build to keep
+things simple.
+
+Here are the steps for building in release mode with a single-configuration
+generator, like the Unix Makefiles one:
+
+```sh
+cmake -S . -B build -D CMAKE_BUILD_TYPE=Release
+cmake --build build
+```
+
+Here are the steps for building in release mode with a multi-configuration
+generator, like the Visual Studio ones:
+
+```sh
+cmake -S . -B build
+cmake --build build --config Release
+```
+
+### Building with MSVC
+
+Note that MSVC by default is not standards compliant and you need to pass some
+flags to make it behave properly. See the `flags-windows` preset in the
+[CMakePresets.json](CMakePresets.json) file for the flags and with what
+variable to provide them to CMake during configuration.
+
+### Building on Apple Silicon
+
+CMake supports building on Apple Silicon properly since 3.20.1. Make sure you
+have the [latest version][1] installed.
+
+## Install
+
+This project doesn't require any special command-line flags to install to keep
+things simple. As a prerequisite, the project has to be built with the above
+commands already.
+
+The below commands require at least CMake 3.15 to run, because that is the
+version in which [Install a Project][2] was added.
+
+Here is the command for installing the release mode artifacts with a
+single-configuration generator, like the Unix Makefiles one:
+
+```sh
+cmake --install build
+```
+
+Here is the command for installing the release mode artifacts with a
+multi-configuration generator, like the Visual Studio ones:
+
+```sh
+cmake --install build --config Release
+```
+
+[1]: https://cmake.org/download/
+[2]: https://cmake.org/cmake/help/latest/manual/cmake.1.html#install-a-project