Add build private vsix to readme

apps/logic-apps-ux-docs/docs/vscode.md

@@ -44,6 +44,14 @@ To debug the app using the common browser's debugging console, for example, usin
 
 For more information, see [debugging Visual Studio Code extensions](https://code.visualstudio.com/docs/editor/debugging).
 
+## Build private vsix
+
+To build a private vsix from the compiled project, follow these steps:
+
+1.  Follow steps 1-3 from Run (Dev/Debug) section. This will compile the project and will update the latest changes for the vsix creation.
+2.  Run the following command: `npm run vscode:designer:pack` in the root folder. This will create a vsix file in `dist` root folder.
+3.  After running the command, you will see the following message: `Packaged: /<repo-path>/LogicAppsUX/dist/apps/vs-code-designer/vscode-azurelogicapps-<extension-version>.vsix` with the exact path where the vsix file is located.
+
 ## App architecture
 
 ![Architecture](./img/architecture.png)