docs: add preview screenshot to readme

Author: shabeeltt

README.md

@@ -12,6 +12,12 @@
 ![Node.js](https://img.shields.io/badge/Node.js-green?logo=node.js)
 ![GraphQL](https://img.shields.io/badge/GraphQL-pink?logo=graphql)
 
+## Preview
+
+<p align="center">
+  <img src="./public/screenshots/screenshot.png" alt="DevImpact comparison tables and analytics chart" width="900">
+</p>
+
 **DevImpact** is an open-source platform that compares software developers based on their real impact in the open-source ecosystem — not just raw numbers.
 
 It evaluates developers using a smart scoring system that considers: