chore: update codelab to say context menus accept html

[BeksOmega]

The basics

• [X] I validated my changes

The details

Resolves

Fixes N/A

Proposed Changes

Updates the context menu codelab to specify that context menu options can be or return HTML.

Reason for Changes

App Inventor has bugged me about the docs being out of date twice now so I'm fixing it.

Test Coverage

N/A

Documentation

This is docs silly!

Additional Information

N/A