Update useScrollbarWidth.story.tsx

[andrewmorgans-razor]

Storybook doc linked to incorrect md file

Description

Updates the useScrollbarWidth story so that it displays the correct documentation

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as before)

Checklist

• Read the Contributing Guide
• Perform a code self-review
• Comment the code, particularly in hard-to-understand areas
• Add documentation
• Add hook's story at Storybook
• Cover changes with tests
• Ensure the test suite passes (yarn test)
• Provide 100% tests coverage
• Make sure code lints (yarn lint). Fix it with yarn lint:fix in case of failure.
• Make sure types are fine (yarn lint:types).