added troubleshooting

README.md

@@ -65,7 +65,11 @@ _OCP CAD Viewer_ for VS Code is an extension to show [CadQuery](https://github.c
    - Install the Python extension in VS Code
    - Continue with 1. above
 
-**Note:** Do not use the _OCP CAD Viewer_ logo to verify your _OCP CAD Viewer_ settings! The logo overwrites all your settings in VS Code with its own settings to always look the same on each instance. Use a simple own model for checking your conmfiguration
+**Notes:** 
+
+- Do not use the _OCP CAD Viewer_ logo to verify your _OCP CAD Viewer_ settings! The logo overwrites all your settings in VS Code with its own settings to always look the same on each instance. Use a simple own model for checking your conmfiguration
+
+- If you run into issues, see [Troubleshooting](#troubleshooting)
 
 ## Usage
 
@@ -272,6 +276,24 @@ NATIVE_TESSELLATOR=1 OCP_VSCODE_PYTEST=1 pytest -v -s pytests/
 
 ## Troubleshooting
 
+- **Generic ("it doesn't work")**
+
+  1) Confirm that VS Code extension and ocp_vscode have the same version. This can be seen in the OCP CAD Viewer UI. Or alternatively in the Output panel of VS Code:
+
+      ```text
+      [19:56:07.114} INFO  ] ocp_vscode library version 2.6.1 matches extension version 2.6.1
+      ```
+
+  2) Test whether the standalone viewer works, see [Standalone mode](#standalone-mode) (to eliminate VS Code issues)
+  3) Open a work folder and not a Python file (to ensure we do not get in Python path problems)
+  4) Check the Output panel. Search for:
+      - `PythonPath: 'aaa/bbb/python'` **=> right Python environment?**
+      - `Server started on port xxxx` (or so) **=> right port? default is 3939**
+      - `Starting Websocket server` **=> should not be followed by an error**
+      - `OCP Cad Viewer port: xxxx, folder: yyyy zzzz` **=> yyyy should be the right working folder?**
+  5) If all looks fine until now, then toggle Developer tools in VS Code and check browser console. Often we see a WebGL error for the browser of VS Code used for the viewer.
+
+
 - **CAD Models almost always are invisible in the OCP viewer window**
 
   ```bash