docs: add GitHub Pages landing page (docs/index.md)

- Includes quick links to server/client adoption guides
- Adds Quick Start and “where to find generated wrappers”
- Lightweight landing page for GitHub Pages

Author: barissayli

docs/index.md

@@ -0,0 +1,34 @@
+# Spring Boot OpenAPI Generics Clients
+
+Welcome! 👋
+
+This site is generated from the [`spring-boot-openapi-generics-clients`](https://github.com/bsayli/spring-boot-openapi-generics-clients) repository.
+
+---
+
+## 📘 Adoption Guides
+
+* [Server-Side Adoption](adoption/server-side-adoption.md)
+* [Client-Side Adoption](adoption/client-side-adoption.md)
+
+---
+
+## 🚀 Quick Start
+
+```bash
+cd customer-service
+mvn spring-boot:run
+
+cd ../customer-service-client
+mvn clean install
+```
+
+Generated wrappers can be found under:
+
+`target/generated-sources/openapi/src/gen/java`
+
+---
+
+## 📖 More Docs
+
+See the full [README on GitHub](https://github.com/bsayli/spring-boot-openapi-generics-clients#readme).