docs(fs): add zfs comment regarding pool creation

global/fs/zfs.nix

@@ -4,6 +4,9 @@
 , ... }: with lib; let
   cfg = config.global.fs;
 in {
+  # -o ashift=12
+  # -O encryption=on -O keyformat=passphrase -O keylocation=prompt
+  # -O compression=on -O mountpoint=none -O xattr=sa -O acltype=posixacl
   options.global.fs.zfs = {
     persist = mkOption {
       type = with types; str;