Update README.md

Author: adamgeorge309

README.md

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 Visual Studio Code extension for the OMNeT++ NED and MSG languages.
 
-[Download latest release](https://github.com/omnetpp/omnetpp-vscode/releases/latest) or build locally.
+The extension is available in the [VS Code Marketplace](https://marketplace.visualstudio.com/items?itemName=opensim.omnetpp-vscode).
+
+Alternatively, [Download latest release](https://github.com/omnetpp/omnetpp-vscode/releases/latest) or build locally.
 
 ## Features