Sys prefix by default

Author: SylvainCorlay

README.md

@@ -13,7 +13,7 @@ Using pip:
 
 ```
 pip install pythreejs
-jupyter nbextension enable --py pythreejs
+jupyter nbextension enable --py --sys-prefix pythreejs
 ```
 
 Using conda
@@ -28,8 +28,8 @@ For a development installation (requires npm):
 $ git clone https://github.com/jovyan/pythreejs.git
 $ cd pythreejs
 $ pip install -e .
-$ jupyter nbextension install --py --symlink --user pythreejs
-$ jupyter nbextension enable --py --user pythreejs
+$ jupyter nbextension install --py --symlink --sys-prefix pythreejs
+$ jupyter nbextension enable --py --sys-prefix pythreejs
 ```
 
 Note for developers: the `--symlink` argument on Linux or OS X allows one to