How to install package from github?

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3 
  buildPhase = ''
    nix-build ${src}/release.nix
  '';

You don’t want to nix-build while building a derivation. For future reference what you want to do is commonly known as “Import From Derivation” (IFD), and it is pretty much what it sounds like:

let src = pkgs.fetchFromGitHub {
    owner  = "awakesecurity";
    repo   = "hocker";
    rev    = "88150c7b8a0664a70757ffd88b2ac12b84dd0604";
    sha256 = "1mb3gfg01mj7ajjl1ylw24mnwamcnnifbxkakzal2j6ibqyqw6rq";
  };
in
import "${src}/release.nix"

(or use callPackage instead of import if you need)

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