Fix broken Azure Functions logo URL in README

[Copilot]

The Azure Functions logo in the README was not displaying due to a broken URL reference. The old URL was pointing to a path that no longer exists in the azure-functions-cli repository.

Issue: The logo reference was using:

https://raw.githubusercontent.com/Azure/azure-functions-cli/master/src/Azure.Functions.Cli/npm/assets/azure-functions-logo-color-raster.png

This URL returns a 404 Not Found error, causing the logo to not display in the README.

Fix: Updated the logo URL to the correct path:

https://raw.githubusercontent.com/Azure/azure-functions-cli/refs/heads/main/eng/res/functions.png

This URL returns a valid PNG image and displays correctly.

The change is minimal and only affects the documentation - no code changes were made.

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.