Updated SC2304 (markdown)

SC2304.md

@@ -17,6 +17,8 @@ result=$(expr 2 \* 3)
 ```
 ### Rationale:
 
+ShellCheck found an `expr` command whose operator is an unescaped asterisk `*`.
+
 When using `expr`, each argument is expanded the same way as for any other command. This means that `expr 2 * 3` will turn into `expr 2 Desktop Documents Downloads Music Pictures 3` depending on the files in the current directory, causing an error like `expr: syntax error: unexpected argument ‘Desktop’`
 
 The best way to avoid this is to avoid `expr` and instead use `$((..))` instead. If you for any reason prefer the 200x slower, heavyweight process of forking a new process, you can escape the `*`. Both ways are demonstrated in the correct example.