1) Download an extension called 'get cookies.txt'.
   1.1) Google Chrome: https://chromewebstore.google.com/detail/get-cookiestxt-locally/cclelndahbckbenkjhflpdbgdldlbecc
   1.2) Firefox: https://addons.mozilla.org/en-US/firefox/addon/cookies-txt/
   You can skip downloading it if you don't want to play age-restricted videos (some music video clips and other stuff marked 'not for kids').
   Also, YouTube started actively blocking video downloads, so you might get an error "Sign in to confirm you're not a bot".
   In this case, cookies also help, but I heard that you might get your YouTube account banned. So use with caution.
2) Create your discord bot on 'https://discord.com/developers/applications'.
3) Enter your discord bot token in token.txt
4) chmod +x start.sh && ./start.sh
5) Invite your bot to your server.