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

docs_src/session_groups/tutorial004.py

@@ -0,0 +1,26 @@
+import asyncio
+
+from mcp_types import Implementation
+
+from mcp import ClientSessionGroup, StdioServerParameters
+
+
+def by_server(name: str, server_info: Implementation) -> str:
+    return f"{server_info.name}.{name}"
+
+
+async def main() -> None:
+    library = StdioServerParameters(command="uv", args=["run", "mcp", "run", "library_server.py"])
+    web = StdioServerParameters(command="uv", args=["run", "mcp", "run", "web_server.py"])
+
+    async with ClientSessionGroup(component_name_hook=by_server) as group:
+        await group.connect_to_server(library)
+        await group.connect_to_server(web)
+
+        print(sorted(group.tools))
+        result = await group.call_tool("Web.search", {"query": "model context protocol"})
+        print(result.structured_content)
+
+
+if __name__ == "__main__":
+    asyncio.run(main())