Update README.md

README.md

 # Stable Diffusion web UI
 A browser interface based on Gradio library for Stable Diffusion.
 
-![](txt2img_screenshot.png)
+![](txt2img_Screenshot.png)
 
 ## Features
 [Detailed feature showcase with images](https://github.com/AUTOMATIC1111/stable-diffusion-webui/wiki/Features):