Update logo path in README and remove old asset

Changed the image path in README.md to point to docs/assets/spectrumlab.svg and deleted the obsolete assets/spectrumlab.svg file.

Author: little1d

README.md

@@ -1,7 +1,7 @@
 <!-- # SpectrumLab -->
 
 <div align="center">
-  <img src="assets/spectrumlab.svg" alt="SpectrumLab" width="600"/>
+  <img src="docs/assets/spectrumlab.svg" alt="SpectrumLab" width="600"/>
 
   <p><strong>A pioneering unified platform designed to systematize and accelerate deep learning research in spectroscopy.</strong></p>
 </div>