Update welcome-message.txt

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.devcontainer/welcome-message.txt

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 👋 Welcome to building a full stack fitness application with GitHub Copilot! We are thrilled that you are here and we hope you are excited to explore the capabilities of Copilot!
 📝 If you would like to sign up for Copilot visit here: https://github.com/features/copilot#pricing
-📃 GitHub Copilot documentation: https://docs.github.com/en/copilot
+📃 GitHub Copilot documentation: https://docs.github.com/en/copilot