NixOS: upgrade to release 21.11 with ZFS 2.1.1

Signed-off-by: Maurice Zhou <jasper@apvc.uk>

docs/Getting Started/NixOS/Root on ZFS/1-preparation.rst

@@ -7,7 +7,7 @@ Preparation
    :local:
 
 #. Download `Minimal ISO image
-   <https://channels.nixos.org/nixos-21.05/latest-nixos-minimal-x86_64-linux.iso>`__ and boot from it.
+   <https://channels.nixos.org/nixos-21.11/latest-nixos-minimal-x86_64-linux.iso>`__ and boot from it.
 
 #. Connect to network. See `NixOS manual <https://nixos.org/manual/nixos/stable/index.html#sec-installation-booting>`__.
 

docs/Getting Started/NixOS/Root on ZFS/2-system-configuration.rst

@@ -49,17 +49,7 @@ System Configuration
 
 
     zpool create \
-    -d -o feature@async_destroy=enabled \
-    -o feature@bookmarks=enabled \
-    -o feature@embedded_data=enabled \
-    -o feature@empty_bpobj=enabled \
-    -o feature@enabled_txg=enabled \
-    -o feature@extensible_dataset=enabled \
-    -o feature@filesystem_limits=enabled \
-    -o feature@hole_birth=enabled \
-    -o feature@large_blocks=enabled \
-    -o feature@lz4_compress=enabled \
-    -o feature@spacemap_histogram=enabled \
+        -o compatibility=grub2 \
         -o ashift=12 \
         -o autotrim=on \
         -O acltype=posixacl \