Share a link from README.md to the deployed Jetton in CI

[novusnota]

After deployment, CI can compose a self-contained index.html page with an actual link to the deployed Jetton on the testnet.

This would require enabling GitHub Pages and adding a link to it from the README.md, which can be a badge.

And, perhaps, we could link GitHub Pages from the repository itself too, because said index.html might also contain useful dev docs which are better presented on the website and not in README.