blackbox: add homepage

pkgs/applications/version-management/blackbox/default.nix

···
 
   meta = with lib; {
     description = "Safely store secrets in a VCS repo";
+    homepage = "https://github.com/StackExchange/blackbox";
     maintainers = with maintainers; [ ericsagnes ];
     license = licenses.mit;
     platforms = platforms.all;