Add "Back to top" links to each section in README.md

[rvqzs]

Description

I have added "Back to top" links beneath each h2 and h3 header in the README.md file to enhance navigation. These links allow users to quickly return to the "Table of Contents" section without needing to scroll manually.

Demo

Motivation and Context

This change improves user experience by making it easier to navigate through the document. The addition of "Back to top" links is especially helpful for longer sections, saving users time and effort when reviewing content.

How Has This Been Tested?

1. Clicking each "Back to top" link to ensure they navigate back to the "Table of Contents" section.
2. Ensured that links are displayed correctly across different Markdown viewers (GitHub, local Markdown viewers, etc.).
3. Reviewed the Markdown file to confirm that no other content was affected.

Types of changes

• Content Update (change which fixes an issue or updates an already existing submission)
• New Article (change which adds functionality)
• Documentation change

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have made checks to ensure URLs and other resources are valid