README: Open VSX Registry

Author: joshtynjala

README.md

@@ -1,6 +1,6 @@
 # ActionScript & MXML extension for Visual Studio Code
 
-This README file is intended for contributors to the extension. If you simply want to install the latest stable version of the extension, please visit the [Visual Studio Marketplace](https://marketplace.visualstudio.com/items?itemName=bowlerhatllc.vscode-as3mxml). For help using the extension, visit the [vscode-as3mxml wiki](https://github.com/BowlerHatLLC/vscode-as3mxml/wiki) for detailed instructions.
+This README file is intended for contributors to the extension. If you simply want to install the latest stable version of the extension, please visit the [Visual Studio Marketplace](https://marketplace.visualstudio.com/items?itemName=bowlerhatllc.vscode-as3mxml) or the [Open VSX Registry](https://open-vsx.org/extension/bowlerhatllc/vscode-as3mxml). For help using the extension, visit the [vscode-as3mxml wiki](https://github.com/BowlerHatLLC/vscode-as3mxml/wiki) for detailed instructions.
 
 ## Modules