Add note on alternative bell character in course-definition.yml

Include guidance for using '\u0007' as an alternative to '\a' for languages that do not support the latter in the shell completion section.

Author: andy1li

course-definition.yml

@@ -1048,6 +1048,10 @@ stages:
       The tester will verify that your shell does not attempt completion on invalid commands, the bell is sent.
       The bell is sent by printing the `\a` character.
 
+      ### Notes:
+
+      - If `\a` is not supported in the language you're using, you can use `\u0007` instead.
+
     marketing_md: |-
       In this stage, you'll implement support for handling invalid commands gracefully.