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

docs_src/structured_output/tutorial002.py

@@ -0,0 +1,17 @@
+from pydantic import BaseModel, Field
+
+from mcp.server import MCPServer
+
+mcp = MCPServer("Weather")
+
+
+class WeatherData(BaseModel):
+    temperature: float = Field(description="Degrees Celsius.")
+    humidity: float = Field(description="Relative humidity, 0 to 1.")
+    conditions: str
+
+
+@mcp.tool()
+def get_weather(city: str) -> WeatherData:
+    """Current weather for a city."""
+    return WeatherData(temperature=16.2, humidity=0.83, conditions="Overcast")