docs: fix a broken link (close: #1020)

Author: ulivz

Diff for: packages/docs/docs/config/README.md

@@ -168,7 +168,7 @@ Specify this to use a custom theme.
 
 **Also see:**
 
-- [Using a theme](../theme/README.md#using-a-theme).
+- [Using a theme](../theme/using-a-theme.md).
 
 ### themeConfig
 
@@ -188,7 +188,7 @@ Provide config options to the used theme. The options will vary depending on the
 - Type: `Object|Array`
 - Default: `undefined`
 
-Please refer to [Plugin > Using a plugin](../plugin/README.md#using-a-plugin) to learn how to use a plugin.
+Please refer to [Plugin > Using a plugin](../plugin/using-a-plugin.md) to learn how to use a plugin.
 
 ## Markdown
 

Diff for: packages/docs/docs/zh/config/README.md

@@ -162,7 +162,7 @@ VuePress provides a convenient way to add extra styles. you can create an `.vuep
 
 **参考:**
 
-- [Using a theme](../theme/README.md#using-a-theme).
+- [使用主题](../theme/using-a-theme.md).
 
 ### themeConfig
 
@@ -182,7 +182,7 @@ VuePress provides a convenient way to add extra styles. you can create an `.vuep
 - Type: `Object|Array`
 - Default: `undefined`
 
-请参考 [plugin > Using a plugin](../plugin/README.md#using-a-plugin) 来使用一个插件。
+请参考 [plugin > Using a plugin](../plugin/using-a-plugin.md) 来使用一个插件。
 
 ## Markdown