docs: add CI status badge to README

Author: CarlosGamez-Nova

README.md

@@ -1,5 +1,7 @@
 # zod-to-d2
 
+[![CI](https://github.com/EngineersTools/zod-to-d2/actions/workflows/ci.yml/badge.svg)](https://github.com/EngineersTools/zod-to-d2/actions/workflows/ci.yml)
+
 `zod-to-d2` is a TypeScript library that extends the [Zod](https://github.com/colinhacks/zod) schema validation library, enabling you to annotate your schemas and automatically generate [D2](https://d2lang.com/) diagrams. This helps visualize data models, relationships, and schema structures directly from your Zod definitions.
 
 ## Features