📝 Add documentation about settings and env vars (#1118)

* Add doc and example for env var config

* Syntax highlight for .env file

* Add test for configuration docs

* 📝 Update settings docs, add more examples

* ✅ Add tests for settings

* 🚚 Rename "Application Configuration" to "Metadata and Docs URLs"

to disambiguate between that and settings

* 🔥 Remove replaced example file

Co-authored-by: Sebastián Ramírez <tiangolo@gmail.com>

docs_src/settings/tutorial001.py

@@ -0,0 +1,21 @@
+from fastapi import FastAPI
+from pydantic import BaseSettings
+
+
+class Settings(BaseSettings):
+    app_name: str = "Awesome API"
+    admin_email: str
+    items_per_user: int = 50
+
+
+settings = Settings()
+app = FastAPI()
+
+
+@app.get("/info")
+async def info():
+    return {
+        "app_name": settings.app_name,
+        "admin_email": settings.admin_email,
+        "items_per_user": settings.items_per_user,
+    }