Added demo video to README.md

Author: kazuyaseki

README.md

@@ -10,6 +10,10 @@ Figma Plugin to generate code using OpenAI API.
 
 NOTE: as of right now, OpenAI API does not seem to generate code in good quality with gpt-3.5-turbo.
 
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+https://user-images.githubusercontent.com/6080698/234930449-b5b0f3cb-2d82-454c-be57-4dd4f969942f.mp4
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 ## To Develop
 
 First create .env file and set your OpenAI API key and GitHub API key, repository owner and name where you would want to push result code.