feat: update workspace paths and enhance gitignore

- Updated stablediffusion crate path from "../stable-diffusion-burn" to "./crates/stable-diffusion-burn" for proper workspace resolution
- Enhanced .gitignore to include generated model files (.mpk, .pt, .bin, .safetensors, .ckpt) and user_data directory
- Added Cargo.lock to gitignore with appropriate comment
- Reorganized IDE files section in gitignore for better clarity
- Added newline at end of file for proper formatting

crates/stable-diffusion-burn/burn-crates/burn-autodiff/README.md

@@ -0,0 +1,8 @@
+# Burn Autodiff
+
+> [Burn](https://github.com/tracel-ai/burn) autodiff backend
+
+[![Current Crates.io Version](https://img.shields.io/crates/v/burn-autodiff.svg)](https://crates.io/crates/burn-autodiff)
+[![license](https://shields.io/badge/license-MIT%2FApache--2.0-blue)](https://github.com/tracel-ai/burn-autodiff/blob/master/README.md)
+
+For now only first order reverse mode autodiff is supported.