add usage hint

README.md

@@ -4,6 +4,12 @@ This utility is a proxy for `poweroff` to prevent you from accidentally shutting
 the wrong system.  It does this by printing a warning message and asking for confirmation
 followed by a countdown before executing the actual command.
 
+It is most useful when creating an alias for `poweroff` in your shell, like:
+
+```sh
+alias poweroff=/usr/local/sbin/poweroff_guard
+```
+
 ## Important Consideration
 
 If the standard output is not a tty, this behaves exactly like the regular `poweroff`.