docs: add hardware variability disclaimer to performance benchmarks in README

README.md

@@ -66,7 +66,7 @@ local-ai-image-generator/
 
 ## ⏱️ Performance Benchmarks
 
-Typical generation times for an image with **20 steps** (e.g. 512x512 resolution):
+Typical generation times for an image with **20 steps** (e.g. 512x512 resolution; actual times can vary depending on specific hardware specifications, clock speeds, and system load):
 
 *   **CUDA GPU (Nvidia RTX):** ~10 seconds.
 *   **Vulkan GPU (AMD / Intel Arc):** ~89 seconds.