sops: set meta.mainProgram

This allows things like `lib.getExe sops` to get the path of the `sops`
executable.

pkgs/tools/security/sops/default.nix

@@ -21,6 +21,7 @@ buildGoModule rec {
     homepage = "https://github.com/getsops/sops";
     description = "Simple and flexible tool for managing secrets";
     changelog = "https://github.com/getsops/sops/blob/v${version}/CHANGELOG.rst";
+    mainProgram = "sops";
     maintainers = [ maintainers.marsam ];
     license = licenses.mpl20;
   };