insert output of the cli --help

README.md

@@ -34,7 +34,32 @@ TODO: link to generated module options
 
 ### CLI
 
-TODO: output of the cli --help
+```
+$ nix run github:nix-community/disko --
+
+disko [options] disk-config.nix
+or disko [options] --flake github:somebody/somewhere
+
+Options:
+
+* -m, --mode mode
+  set the mode, either create or mount
+* -f, --flake uri
+  fetch the disko config relative to this flake's root
+* --arg name value
+  pass value to nix-build. can be used to set disk-names for example
+* --argstr name value
+  pass value to nix-build as string
+* --root-mountpoint /mnt
+  where to mount the device tree
+* --dry-run
+  just show the path to the script instead of running it
+* --debug
+  run with set -x
+
+```
+
+
 
 ## Installing NixOS module