Explicitly add missing opacity-0 helper class example for clarity.

[Hopiu]

Description

Add a missing opacity-0 helper class example.

Motivation & Context

From the existing examples, it wasn't obvious to me that this class exists. This commit makes it a bit more explicit. It adds an example to the documentation, nothing more.

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed