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

docs_src/client_transports/tutorial003.py

@@ -0,0 +1,16 @@
+import httpx
+
+from mcp import Client
+from mcp.client.streamable_http import streamable_http_client
+
+
+async def main() -> None:
+    async with httpx.AsyncClient(
+        headers={"Authorization": "Bearer ..."},
+        timeout=httpx.Timeout(30.0, read=300.0),
+        follow_redirects=True,
+    ) as http_client:
+        transport = streamable_http_client("http://localhost:8000/mcp", http_client=http_client)
+        async with Client(transport) as client:
+            result = await client.list_tools()
+            print([tool.name for tool in result.tools])