Minor update to installation instructions.

Removed the conjunction 'or', because there is no previous installation option.

Author: tylere

README.md

@@ -9,7 +9,7 @@ A sidecar output widget for JupyterLab
 
 ## Installation
 
-Or, if you use jupyterlab:
+If you use jupyterlab:
 
 ```bash
 pip install sidecar