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

docs_src/client_transports/tutorial002.py

@@ -0,0 +1,7 @@
+from mcp import Client
+
+
+async def main() -> None:
+    async with Client("http://localhost:8000/mcp") as client:
+        result = await client.list_tools()
+        print([tool.name for tool in result.tools])