Add 'Neovim from Scratch' Tutorial

Add [ChrisAtMachine - Neovim from Scratch](https://youtube.com/playlist?list=PLhoH5vyxr6Qq41NFL4GvhFp-WLd5xzIzZ) YouTube tutorial playlist to 'Existing tutorials for writing Lua in Neovim' README section.

- [ChrisAtMachine - Neovim from Scratch (YouTube Playlist)](https://www.youtube.com/playlist?list=PLhoH5vyxr6Qq41NFL4GvhFp-WLd5xzIzZ)
- [ChrisAtMachine - Neovim from Scratch (GitHub)](https://github.com/LunarVim/Neovim-from-scratch)

README.md

@@ -44,6 +44,7 @@ A few tutorials have already been written to help people write plugins in Lua. S
 - [Building A Vim Statusline from Scratch - jdhao's blog](https://jdhao.github.io/2019/11/03/vim_custom_statusline/)
 - [Configuring Neovim using Lua](https://icyphox.sh/blog/nvim-lua/)
 - [Devlog | Everything you need to know to configure neovim using lua](https://vonheikemen.github.io/devlog/tools/configuring-neovim-using-lua/)
+- [ChrisAtMachine - Neovim from Scratch](https://youtube.com/playlist?list=PLhoH5vyxr6Qq41NFL4GvhFp-WLd5xzIzZ)
 
 ### Companion plugins