README.md: add Nix to the linux package managers

Author: WilliButz

README.md

@@ -70,6 +70,7 @@ From there:
 ### From Linux package managers
 
 - [Arch Linux](#arch-linux)
+- [Nix](#nix)
 - [Snap](#snap)
 
 #### Arch Linux
@@ -83,6 +84,12 @@ Development version of go-ipfs is also on AUR under
 [go-ipfs-git](https://aur.archlinux.org/packages/go-ipfs-git/).
 You can install it using your favourite AUR Helper or manually from AUR.
 
+### Nix
+
+For Linux and MacOSX you can use the purely functional package manager [Nix](https://nixos.org/nix/):
+
+    $ nix-env -i ipfs
+
 #### Snap
 
 With snap, in any of the [supported Linux distributions](https://snapcraft.io/docs/core/install):