Simplifying eoc installation for users of the nix package manager

[morphqdd]

As a user of the NixOS operating system, I encountered a problem installing eoc via npm. This is due to how the nix package manager stores packages, which makes global installation via npm impossible.

Attempting to use bun instead of npm also did not produce the desired result. Since bun was unable to pull in the necessary dependencies, the basic example from README.md did not compile.

I want to write a flake.nix file that will simplify the installation of eoc for users of both NixOS and the Nix package manager in general. I also want to add a new installation method to README.md.