Update README.md

Author: rodvrees

README.md

@@ -11,6 +11,9 @@ It is able to accurately predict CCS for modified peptides, even if the modifica
 Install with pip:
 `pip install im2deep`
 
+If you want to use the multi-output model for CCS prediction of multi-conformational peptide ions, use the following installation command:
+`pip install 'im2deep[er]'`
+
 ## Usage
 ### Basic CLI usage:
 ```sh