Make README more approachable for smart contract devs

### What is wrong?

Please include information like:

Per [this](https://news.ycombinator.com/item?id=29449956) comment on Hacker News, it is not necessarily obvious to a prospective Fe adopter why they should use Fe over Solidity or Vyper.

The way to address this problem likely differs based on whether the prospective adopter is already experienced with SC development.

### How can it be fixed

I agree with the commenter here that we need to make the answers to the following questions quickly discoverable for visitors. After all, developers don't want to be detectives when they don't need to be (we all get enough of that during debugging). We need to classify and communicate the "concrete improvements"
1. Ergonomics
2. Performance
3. Security
4. "Analyzability"

I can think of multiple examples which fit into each of these categories. There can be more categories in the classification as well, of course. Regardless, for each major improvement in each of the categories, we ought to describe what's different and provide a canonical example which demonstrates that difference.

Start with the repository README and review how it currently explains Fe to prospective users. Research the concrete differences from Solidity and Vyper across ergonomics, performance, security, and analyzability, then define canonical examples that make those comparisons quickly discoverable. Done means the README clearly communicates these improvements for both experienced and new smart contract developers.

Written by the indexing model from the issue text.