docs(blog): post about rust-gcd

[abentkamp]

This is a blog post about my GCD experiments.

What's not in this post:

• Verifying binary GCD in Aeneas
• Hax/Lean
• Functional correctness

The first two would probably make sense to add into this first blog post? For functional correctness, the plan is to have a second blog post.

You can view the blog in the browser by running just docs.

[skip changelog]