missing instruction in install procedure

README.md

@@ -25,7 +25,7 @@ curl -L  https://github.com/nix-community/nix-user-chroot/releases/download/1.2.
 # give exec rights
 chmod u+x nix-user-chroot
 # download and install nix
-./nix-user-chroot ~/.nix bash -c "curl -L https://nixos.org/nix/install | bash"
+mkdir -p ~/.nix && ./nix-user-chroot ~/.nix bash -c "curl -L https://nixos.org/nix/install | bash"
 # enable cachix
 mkdir -p ~/.config/nix && cp ~/RM4ES-practicals/util/nix.conf ~/.config/nix
 # add a line to your bashrc