Move requirements into their own directory (#12547)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

docs/source/getting_started/installation/cpu/apple.inc.md

@@ -25,7 +25,7 @@ After installation of XCode and the Command Line Tools, which include Apple Clan
 ```console
 git clone https://github.com/vllm-project/vllm.git
 cd vllm
-pip install -r requirements-cpu.txt
+pip install -r requirements/cpu.txt
 pip install -e . 
 ```