Add blockchain course (#10841)

* Add blockchain course

* Add blockchain course

* Update courses/free-courses-en.md

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Co-authored-by: Eric Hellman <eric@hellman.net>

courses/free-courses-en.md

@@ -316,6 +316,7 @@
 * [Build an IoT Blockchain Network for a Supply Chain](https://cognitiveclass.ai/courses/blockchain-iot-node-red-food-network) - CognitiveClass.ai
 * [Build and Deploy Your First Decentralized App with Etherem](https://www.udemy.com/course/your-first-decentralized-app/) - Gary Simon (Udemy)
 * [CryptoZombies.io](https://cryptozombies.io) - CleverFlare, Loom Network
+* [Learn Blockchain](https://www.youtube.com/playlist?list=PLlp912GlUiC1xPnwVmKgIiuMERetMwre9) - Roomyan
 * [Solidity, Blockchain, and Smart Contract Course – Beginner to Expert Python Tutorial](https://www.youtube.com/watch?v=M576WGiDBdQ) - Patrick Collins (freeCodeCamp.org)