updated env example

.env.example

@@ -1,2 +1,11 @@
-DATABASE_URI=mongodb://127.0.0.1/your-database-name
+POSTGRES_DB=DB_NAME
+POSTGRES_USER=USER
+POSTGRES_PASSWORD=PASSWORD
+# Database connection string
+DATABASE_URI=postgres://${POSTGRES_USER}:${POSTGRES_PASSWORD}@127.0.0.1:5432/${POSTGRES_DB}
+
+# Payload
 PAYLOAD_SECRET=YOUR_SECRET_HERE
+PREVIEW_SECRET=YOUR_SECRET_HERE
+
+NEXT_PUBLIC_SERVER_URL=http://localhost:3000