[Doc] Intended links Python multiprocessing library (vllm-project#11878)

Signed-off-by: Isotr0py <[email protected]>

Author: guspan-tanadi

docs/source/design/multiprocessing.md

@@ -21,7 +21,7 @@ This document describes how vLLM deals with these challenges.
 
 ## Multiprocessing Methods
 
-[Python multiprocessing methods](https://docs.python.org/3/library/multiprocessing.html.md#contexts-and-start-methods) include:
+[Python multiprocessing methods](https://docs.python.org/3/library/multiprocessing.html#contexts-and-start-methods) include:
 
 - `spawn` - spawn a new Python process. This will be the default as of Python
   3.14.