Update README.md

Fixes #108

Adding Cairo Playground https://www.cairo-lang.org/cairovm/

README.md

@@ -75,6 +75,7 @@
 - [Starknet Documentation](https://docs.starknet.io/documentation/) - Official Documentation.
 - [The Starknet Book](https://book.starknet.io/) - In-depth guide.
 - [Cairo Documentation](https://www.cairo-lang.org/docs/index.html) - Official Cairo 1.0 Documentation.
+- [Cairo Playground]( https://www.cairo-lang.org/cairovm/) - Experiment writing Cairo online without deploying a smart contract on Starknet.
 - [The Cairo Book](https://book.cairo-lang.org/) - In-depth guide to Cairo.
 - [YouTube channel](https://www.youtube.com/@starkware_ltd) - Official StarkWare YouTube channel.
 - [Roadmap](https://www.starknet.io/en/roadmap) - What’s coming next for Starknet.