Rebuild the docs around tested examples; shrink README.v2.md to a pitch (#2978)

docs_src/structured_output/tutorial005.py

@@ -0,0 +1,17 @@
+from pydantic import BaseModel
+
+from mcp.server import MCPServer
+
+mcp = MCPServer("Weather")
+
+
+class WeatherData(BaseModel):
+    temperature: float
+    humidity: float
+    conditions: str
+
+
+@mcp.tool()
+def get_forecast(city: str, days: int) -> list[WeatherData]:
+    """Daily forecast for a city."""
+    return [WeatherData(temperature=16.2 + day, humidity=0.83, conditions="Overcast") for day in range(days)]