This project has a blueprint, which is available at https://AlexKontorovich.github.io/PrimeNumberTheoremAnd/web/

For those using github's copilot (free for educators), it's very convenient to have the natural language statements right next to the Lean to be formalized. So we write the blueprint TeX right in the *.lean document, separated by delimiters /-%% text here %%-/ for multi-line and --%% text here for single-line TeX. The code automatically scrapes these and populates the blueprint accordingly.