Added knowledge base on Visual Studio Code

knowledge base/visual studio code.md

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+# Visual Studio Code
+
+## Troubleshooting
+
+### _No extensions found_ when running from source
+
+Check the `extensionsGallery` key in your fork's `product.json` file is using the official marketplace:
+
+```sh
+jq '.extensionsGallery' /usr/lib/code/product.json
+{
+  "serviceUrl": "https://marketplace.visualstudio.com/_apis/public/gallery",
+  "cacheUrl": "https://vscode.blob.core.windows.net/gallery/index",
+  "itemUrl": "https://marketplace.visualstudio.com/items"
+}
+```
+
+and if not, change them.
+
+## Sources
+
+- [using extensions in compiled vscode]
+
+[using extensions in compiled vscode]: https://stackoverflow.com/questions/44057402/using-extensions-in-compiled-vscode#45291490
+
+[official product.json]: https://github.com/Microsoft/vscode/blob/master/product.json