docs(zh): translate 'Part file' in markdown guide (#5391)

Author: lonewolfyx

docs/zh/guide/markdown.md

@@ -779,7 +779,7 @@ export default config
 <!--@@include: ./parts/basics.md-->
 ```
 
-**Part file** (`parts/basics.md`)
+**部分文件** (`parts/basics.md`)
 
 ```md
 Some getting started stuff.
@@ -815,7 +815,7 @@ Can be created using `.foorc.json`.
 <!--@@include: ./parts/basics.md{3,}-->
 ```
 
-**Part file** (`parts/basics.md`)
+**部分文件** (`parts/basics.md`)
 
 ```md
 Some getting started stuff.