docs: optimize source code structure show (#2001) [skip ci]

Author: xrkffgg

docs/guide/build.md

@@ -51,13 +51,13 @@ For example, you can specify multiple Rollup outputs with plugins that are only
 Suppose you have the following source code structure:
 
 ```
-|-package.json
-|-vite.config.js
-|-index.html
-|-main.js
-|-nested/
-|---index.html
-|---nested.js
+├── package.json
+├── vite.config.js
+├── index.html
+├── main.js
+└── nested
+    ├── index.html
+    └── nested.js
 ```
 
 During dev, simply navigate or link to `/nested/` - it works as expected, just like for a normal static file server.