Add missing response_model type hint in example route

docs/msr/first-steps.md

@@ -0,0 +1,13 @@
+from typing import List
+from fastapi import FastAPI
+from pydantic import BaseModel
+
+class Item(BaseModel):
+    name: str
+    price: float
+
+app = FastAPI()
+
+@app.get("/items/", response_model=List[Item])
+async def read_items():
+    return [{"name": "Foo", "price": 50.2}]