Fix markdown links （../book/hooks => ../book/hooks.md）in cookbook setup documentation

Author: jexjws

cookbook/setup.md

@@ -96,11 +96,11 @@ To be most compatible, the `starship` binary will run every prompt render and
 is absolute stateless.
 Nushell, however, is very stateful in a single instance.
 
-[Hooks](../book/hooks) allow registration of
+[Hooks](../book/hooks.md) allow registration of
 custom callback functions.
 In this case, the `pre_prompt` hook is very useful.
 With it, we can export state information as an environment variable, for
-example, what [overlays](../book/overlays) are
+example, what [overlays](../book/overlays.md) are
 currently activated.
 
 ```nu

zh-CN/cookbook/setup.md

@@ -95,9 +95,9 @@ $env.APPDATA
 并且是绝对无状态的。
 然而，Nushell 在单个实例中是非常有状态的。
 
-[钩子](../book/hooks) 允许注册自定义回调函数。
+[钩子](../book/hooks.md) 允许注册自定义回调函数。
 在这种情况下，`pre_prompt` 钩子非常有用。
-有了它，我们可以将状态信息导出为环境变量，例如，当前激活了哪些 [覆层](../book/overlays)。
+有了它，我们可以将状态信息导出为环境变量，例如，当前激活了哪些 [覆层](../book/overlays.md)。
 
 ```nu
 # 使用覆层列表设置 NU_OVERLAYS，对 starship 提示有用