Update index.html to make the text below navbar visible

[Srishti-Chugh]

This PR adjusts the spacing to prevent the text below navbar from being hidden.
The issue #574 was identified on the homepage, where the "Sugar Labs" heading was obscured by the navbar. I've added some spacing to ensure proper visibility.

Changes made:
Increased top margin for the "Sugar Labs" heading to create space between it and the navbar.
Ensured the page remains responsive across various screen sizes.

Screenshots:
Before

After adding margin

Please review this and let me know if any further changes are needed.

[quozl]

• your commit message does not follow our making commits guidance,
• don't say "Update index.html" because it is obvious from the rest of the commit which files you have changed.

[pikurasa]

@Srishti-Chugh I think this is good, but can you make a new PR with James's suggestions?

Part of this is learning best practices, so I think it's worth doing once more, following the guidance.

[pikurasa]

@Srishti-Chugh Will you be working to address James's comments? Please let us know either way.