Add more IJulia troubleshooting information

Author: twavv

docs/src/providers/ijulia.md

@@ -42,6 +42,24 @@ python3 -m pip uninstall webio_jupyter_extension
 
 ### The `webio_jupyter_extension` is installed but not working
 
+First, check if the WebIO extension is properly installed:
+```
+# For classic notebook
+jupyter nbextension list
+# Should include in output:
+#     notebook section
+#       webio-jupyter-nbextension/nbextension  enabled 
+
+# For Jupyter lab
+jupyter labextension list
+# Should include in output:
+#     webio-jupyterlab-provider vX.Y.Z enabled OK (python, webio_jupyter_extension)
+```
+
+If the installation is **NOT** installed, continue reading for troubleshooting steps.
+
+#### 1: Make sure to use same Python/Conda environment for both Jupyter and WebIO
+
 Make sure you've installed the `webio_jupyter_extension` package in the same
 Python or Conda environment that you're using to launch Jupyter.
 
@@ -53,6 +71,45 @@ python3 -m pip install webio_jupyter_extension
 python3 -m jupyterlab
 ```
 
+#### 2: Make sure to be consistent with `--user` pip installations
+The WebIO extension will not be detected if Jupyter is intalled system-wide and
+the WebIO extension is installed in your user installation (or vice-versa). Pip
+might install into the per-user install directory if you use the `--user` flag OR
+if you don't have permission to edit the global installation.pip 
+
+You can determine if this is the case by inspecting where the packages are installed:
+```sh
+# replace "jupyterlab" with "notebook" for classic notebook
+pip3 show jupyterlab | grep -i location
+pip3 show webio_jupyter_extension | grep -i location
+```
+
+If this happens, the easiest solution is to uninstall and reinstall all relevant:
+```
+pip3 uninstall jupyter notebook jupyterlab webio_jupyter_extension
+
+# If you want to install it on a per-user basis, omit the "sudo" and change
+# "install" to "install --user"
+sudo pip3 install jupyter notebook jupyterlab webio_jupyter_extension
+```
+
+**Alternatively:** This problem can be avoided using virtual environments:
+```
+# Create a new virtual environment (you only have to do this once!)
+python3 -m venv venv
+
+# Activate the virtual environment
+. venv/bin/active
+
+# Install Jupyter + WebIO extension (you only have to do this once!)
+pip install notebook jupyterlab webio_jupyter_extension
+
+# Launch jupyter
+jupyter lab  # or jupyter notebook
+```
+If using virtual environments, you must always start Jupyter using a virtual
+environment that has the WebIO extension installed.
+
 ## Still having problems?
 
 Open a [GitHub issue](https://github.com/JuliaGizmos/WebIO.jl/issues/new).