docs(README): add contributors section with contributor graph link (magic-peach#330)

Added a dedicated Contributors section to the README that includes:
- contrib.rocks contributor graph image
- Link to full contributor graph on GitHub
- Note welcoming contributions of all kinds
- Link to CONTRIBUTING.md for getting started

This helps new contributors see the active community and encourages
participation in the project.

Closes magic-peach#234

Co-authored-by: Ved Prakash Arya <vedprakasharya9973@gmail.com>
Co-authored-by: Akanksha Trehun <146705736+magic-peach@users.noreply.github.com>

Author: 3 people

README.md

@@ -348,6 +348,15 @@ Thank you to everyone who has contributed to Reframe! 🎉
 ## Privacy
 
 Reframe processes all videos **100% client-side**. Your video files are never uploaded to any server. You can even use Reframe offline (after first load). The source code is fully open for inspection.
+---
+
+## Contributors
+
+Thanks to all the amazing people who have contributed to Reframe!
+
+[![Contributors](https://contrib.rocks/image?repo=magic-peach/reframe)](https://github.com/magic-peach/reframe/graphs/contributors)
+
+We welcome contributions of all kinds — code, documentation, design, and feedback. Check out our [Contributing Guide](CONTRIBUTING.md) to get started.
 
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