add licence badge

README.md

@@ -4,6 +4,7 @@ JSON language service extracted from VSCode to be reused, e.g in the Monaco edit
 [![npm Package](https://img.shields.io/npm/v/vscode-json-languageservice.svg?style=flat-square)](https://www.npmjs.org/package/vscode-json-languageservice)
 [![NPM Downloads](https://img.shields.io/npm/dm/vscode-json-languageservice.svg)](https://npmjs.org/package/vscode-json-languageservice)
 [![Build Status](https://travis-ci.org/Microsoft/vscode-json-languageservice.svg?branch=master)](https://travis-ci.org/Microsoft/vscode-json-languageservice)
+[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
 
 Why?
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