Normalize README folder tree formatting

README.md

@@ -12,8 +12,8 @@ Place the files in the following folders:
 
 ```
 📂 ComfyUI/
-└── 📂 models/
-    └── 📂 checkpoints/
-        ├── sd21-unclip-h.ckpt
-        └── sd21-unclip-l.ckpt
+├── 📂 models/
+│   ├── 📂 checkpoints/
+│   │   ├── sd21-unclip-h.ckpt
+│   │   └── sd21-unclip-l.ckpt
 ```