✨ Add docs about responses with additional status codes (#156)

* ✨ Add docs about responses with additional status codes

* 📝 Update docs, link to documenting additional responses

tests/test_tutorial/test_additional_status_codes/test_tutorial001.py

@@ -0,0 +1,17 @@
+from starlette.testclient import TestClient
+
+from additional_status_codes.tutorial001 import app
+
+client = TestClient(app)
+
+
+def test_update():
+    response = client.put("/items/foo", json={"name": "Wrestlers"})
+    assert response.status_code == 200
+    assert response.json() == {"name": "Wrestlers", "size": None}
+
+
+def test_create():
+    response = client.put("/items/red", json={"name": "Chillies"})
+    assert response.status_code == 201
+    assert response.json() == {"name": "Chillies", "size": None}