address former split-cell users in readme

README.md

@@ -7,12 +7,23 @@ JupyterLab extension to
 - tag cells so that they use a fraction of the width
 - can replace former 'split-cell' extension in the classic notebook
 
+It was have preferred not to re-use the term 'split', because in jupyterlab *split* already means, well, to split a cell into 2 cells...
+
 ## Requirements
 
 - JupyterLab >= 4.0.0
 
 ## Usage
 
+### as a replacement for for former `split-cell`
+
+there is no button (yet) in this extension to do the equivalent of the former 'split-cell' thing, you can use
+
+- either keyboard Ctrl-\ Ctrl-1 Ctrl-2   (meaning you want to use 1 / 2 of the horizontal space)
+- or type gridwidth in the Palette and pick 1/2
+- or command `gridwidth:toggle-1-2`
+- that you can bind to a keyboard shortcut of your choice
+
 ### available tags:
 
 - `gridwidth-1-2` (50%)