clarify the magic comment

README.md

@@ -134,6 +134,8 @@ fi
 # lots more bash...
 ```
 
+The magic comment looks like `# Provide your_sub_name completions`
+
 Passing the `--complete` flag to this subcommand short circuits the real command, and then runs another subcommand instead. The output from your subcommand's `--complete` run is sent to your shell's autocompletion handler for you, and you don't ever have to once worry about how any of that works!
 
 Run the `init` subcommand after you've prepared your sub to get your sub loading automatically in your shell.