docs: fix dead links and update redirect URLs in README

[aoright]

This PR cleans up the README by:

1. Removing the dead link to Matt Gathu's Rust CLI tutorial (domain offline, no active wayback machine snapshots found).
2. Updating Tomomi Imura's Node.js Facebook Messenger bot tutorial link to the author's active personal blog (girliemac.com) as the old tutorials.botsfloor.com domain is defunct.
3. Updating redirected links for the ATS Functional Blockchain tutorial and C++ Rasterization tutorial to avoid 301 redirects.