Add NixOS example

modules/email/mu4e/README.org

@@ -54,6 +54,17 @@ sudo pacman --noconfirm --needed -S mu
 sudo pacman -S isync  # mbsync
 sudo pacman -S offlineimap
 #+END_SRC
+** NixOS
+#+BEGIN_SRC nix
+environment.systemPackages = with pkgs; [
+    mu
+    # And one of the following
+    isync
+    offlineimap
+];
+#+END_SRC
+
+[[https://github.com/Emiller88/dotfiles/blob/master/modules/shell/mail.nix][An example of setting up mbsync with home-manager]]
 
 * TODO Features