Raku Advent 2021: A long journey to Ethereum signatures

We need to write the article for Raku Advent 2021: https://github.com/Raku/advent/blob/master/raku-advent-2021/authors.md

Let's do this over the next iterations:

1. Write the Table of Contents (TOC)
2. Create a comment for each member of TOC
3. Compile the article and save to advent/2021.md