Merge pull request #503 from jupyterlab/fcollonval-patch-1

Improve troubleshooting following issues

Author: kgryte

README.md

@@ -28,12 +28,45 @@ jupyter lab build
 
 ### Troubleshooting
 
-- When you run JupyterLab, if you can see the Git sidepanel UI but you cannot get it to work, you may need to explicitly enable the serverextension by running:
+Before consulting the following list, be sure the server extension and the frontend extension have the same version by executing the following commands:
 
 ```bash
-jupyter serverextension enable --py jupyterlab_git
+jupyter serverextension list
+jupyter labextension list
 ```
 
+- **Issue**: the Git panel does not recognize that you are in a Git repository.
+
+  Possible fixes:
+  
+  - Be sure to be in a Git repository in the filebrowser tab
+  
+  - Check the server log. If you see a warning with a 404 code similar to:  
+    `[W 00:27:41.800 LabApp] 404 GET /git/server_root?1576081660665`
+    
+    Explicitly enable the server extension by running:
+    ```bash
+    jupyter serverextension enable --py jupyterlab_git
+    ```
+    
+  - If you are using JupyterHub or some other technologies requiring an initialization script which includes the jupyterlab-git extension, be sure to install both the frontend and the server extension **before** launching JupyterLab.
+  
+- **Issue**: the Git panel is not visible.
+
+  Possible fixes:
+  
+  - Check that the JupyterLab extension is installed:
+  
+    ```bash
+    jupyter labextension list
+    ```
+    
+    If you don't see `@jupyterlab/git v...  enabled  OK` in the list, explicitly install the jupyter labextension by running:
+    
+    ```bash
+    jupyter labextension @jupyterlab/git
+    ```
+
 ## Development
 
 ### Contributing