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/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 \