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

docs_src/structured_output/tutorial006.py

@@ -0,0 +1,11 @@
+from mcp.server import MCPServer
+
+mcp = MCPServer("Weather")
+
+READINGS = {"London": 16.2, "Cairo": 34.1, "Reykjavik": 4.4}
+
+
+@mcp.tool()
+def get_temperatures(cities: list[str]) -> dict[str, float]:
+    """Current temperature for each city, in degrees Celsius."""
+    return {city: READINGS[city] for city in cities}