miller: copy manpage to $man

pkgs/tools/text/miller/default.nix

···
     sha256 = "sha256-g2Jnqo3U9acyqohGpcEEogq871qJQTc7k0/oIawAQW8=";
   };
 
+  outputs = [ "out" "man" ];
+
   vendorHash = "sha256-/1/FTQL3Ki8QzL+1J4Ah8kwiJyGPd024di/1MC8gtkE=";
+
+  postInstall = ''
+    mkdir -p $man/share/man/man1
+    mv ./man/mlr.1 $man/share/man/man1
+  '';
 
   subPackages = [ "cmd/mlr" ];