DOC: remove the --user flag from installation instructions

doc/installation.jupyter

@@ -1,5 +1,5 @@
 nbformat 4
-nbformat_minor 2
+nbformat_minor 4
 markdown
     This notebook is part of the `jupyter_format` documentation:
     https://jupyter-format.readthedocs.io/.
@@ -19,15 +19,15 @@ markdown
 
         git clone https://github.com/mgeier/jupyter-format.git
         cd jupyter-format
-        python3 -m pip install -e . --user
+        python3 -m pip install -e .
 
-    If you install it in a virtual environment,
-    you can drop the `--user` option.
+    Depending on your Python installation,
+    you may have to use `python` instead of `python3`.
 
     If you don't need a local Git checkout,
     you can also directly install it with
 
-        python3 -m pip install git+https://github.com/mgeier/jupyter-format.git@master --user
+        python3 -m pip install git+https://github.com/mgeier/jupyter-format.git@master
 markdown
     ## JupyterLab and Classic Notebook Integration
 
@@ -89,6 +89,6 @@ notebook_metadata
       "name": "python",
       "nbconvert_exporter": "python",
       "pygments_lexer": "ipython3",
-      "version": "3.7.2"
+      "version": "3.8.5"
      }
     }