Add comprehensive documentation for SnapForm features and workflows

- Introduced new guides for Depth Plane, Surface, and animation workflows.
- Added installation instructions and FAQs to assist users in setup and troubleshooting.
- Created a quick-start guide for first-time users to convert images to Depth Planes.
- Documented the process for removing backgrounds from images.
- Established a models and storage section to clarify data management.
- Included a stylesheets file for improved documentation styling.
- Updated mkdocs configuration for better navigation and theme settings.

README.md

@@ -2,6 +2,10 @@
 
 SnapForm 是一个 Blender 扩展，可以把一张照片、一段视频或一组序列帧快速变成有真实深度的立体面片。
 
+完整使用说明请从[文档首页](docs/index.md)开始；首次使用请依次阅读
+[安装与首次配置](docs/installation.md)和[五分钟上手](docs/quick-start.md)。
+
+
 ## 它能做什么
 
 - 一键把 Image Empty 转换为立体面片：让 AI 估算深度，或直接用原图作为深度