Add OVSX shield to the readme

Author: darkriszty

README.md

@@ -2,6 +2,7 @@
 
 [![Test Status](https://github.com/darkriszty/MarkdownTablePrettify-VSCodeExt/workflows/Tests/badge.svg)](https://github.com/darkriszty/MarkdownTablePrettify-VSCodeExt/actions)
 [![Visual Studio Code extension](https://img.shields.io/visual-studio-marketplace/v/darkriszty.markdown-table-prettify?color=success&label=VSCode)](https://marketplace.visualstudio.com/items?itemName=darkriszty.markdown-table-prettify)
+[![OVSX](https://img.shields.io/open-vsx/v/darkriszty/markdown-table-prettify?color=success&label=Open%20VSX)](https://open-vsx.org/extension/darkriszty/markdown-table-prettify)
 [![Docker image](https://img.shields.io/docker/v/darkriszty/prettify-md?color=success&label=Docker)](https://hub.docker.com/r/darkriszty/prettify-md/tags?page=1&ordering=last_updated)
 [![NPM package](https://img.shields.io/npm/v/markdown-table-prettify?color=success)](https://www.npmjs.com/package/markdown-table-prettify)