Key point
One job
Your README does the first explanation before anyone reads your code. GitHub says a repository README is often the first item a visitor sees.
Make the first screen answer four things: what it does, why it is useful, how to get started, and where to try it live if you have a demo.
What to include
You do not need a long story. You need a clean path from curiosity to testing.
Use these parts: short summary, why it exists, features, live demo, tech stack, local setup, screenshots, and contact or maintainer note.