Refactor model configuration structure and update README

- Changed the configuration format to use a single 'models' list with entries containing 'url' and 'type'.
- Updated validation logic to ensure 'models' entries are correctly structured.
- Modified download logic to check for existing directories before downloading.
- Revised README to reflect new configuration format and usage instructions.

Signed-off-by: Daniel Henry <iamdanhenry@gmail.com>

config.example.yaml

@@ -4,10 +4,10 @@ huggingface_token: ""   # from https://huggingface.co/settings/tokens
 civitai_token: ""       # from https://civitai.com/user/account
 comfyui_base_dir: "/path/to/ComfyUI"
 
-# Lists of model URLs. Civitai: use API URL or add ?token=... is optional (token from config is used).
+# Single list of models. Each entry: url and type (type = ComfyUI subdir under models/).
+# Civitai: use API URL or add ?token=... is optional (token from config is used).
 # Hugging Face: use resolve/main/... URLs.
-diffusion_models: []
-text_encoders: []
-vaes: []
-upscale_models: []
-loras: []
+# models:
+#   - url: "https://..."
+#     type: loras
+models: []