Update README.md

Slicer extension documentation.

Author: marcniethammer

README.md

@@ -250,7 +250,7 @@ We also provide a [colab](https://colab.research.google.com/drive/1JuFL113WN3FHC
 
 ## Slicer Extension
 
-A Slicer extensions is available [here](https://github.com/uncbiag/SlicerUniGradICON?tab=readme-ov-file) (and hopefully will soon be available via the Slicer Extension Manager).
+A Slicer extensions is available [here](https://github.com/uncbiag/SlicerUniGradICON?tab=readme-ov-file) . It is an official Slicer Extension and can be installed via the Slicer Extension Manager. This requires Slicer >=5.7.0. Please make sure to install the Slicer PyTorch extension before as uniGradICON depends on it.
 
 ## Plays well with others