✨ Add docs and tests for Jinja2 templates (#186)

* ✨ Add docs and tests for Jinja2 templates

* 🎨 Fix format in test, remove unused import

tests/test_tutorial/test_templates/test_tutorial001.py

@@ -0,0 +1,19 @@
+import shutil
+
+from starlette.testclient import TestClient
+
+
+def test_main():
+    shutil.copytree("./docs/src/templates/templates/", "./templates")
+    shutil.copytree("./docs/src/templates/static/", "./static")
+    from templates.tutorial001 import app
+
+    client = TestClient(app)
+    response = client.get("/items/foo")
+    assert response.status_code == 200
+    assert b"<h1>Item ID: foo</h1>" in response.content
+    response = client.get("/static/styles.css")
+    assert response.status_code == 200
+    assert b"color: green;" in response.content
+    shutil.rmtree("./templates")
+    shutil.rmtree("./static")