fix(#741): Added the ability to install the eoc package using flake.nix

[morphqdd]

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This pr adds flake.nix for installing eoc via the nix package manager.

It also adds flake.lock to freeze the versions of nix tools used for installation and updates REUSE.toml to ignore the presence of license headers in flake.lock, as it is generated automatically and contains only meta information for building, similar to package.lock.json.

README.md has also been updated, and a new way to download via nix has been added.