Add video tutorial

ch01/README.md

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 # Chapter 1: Understanding Large Language Models
 
 There is no code in this chapter.
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+<br>
+As optional bonus material, below is a video tutorial where I explain the LLM development lifecycle covered in this book:
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+<br>
+<br>
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+[![Link to the video](https://img.youtube.com/vi/kPGTx4wcm_w/0.jpg)](https://www.youtube.com/watch?v=kPGTx4wcm_w)
+