Move changelog to be packaged with extension

README.md

@@ -4,6 +4,8 @@ This project is an extension for Visual Studio Code that adds rich language supp
 
 The extension is released. You can download it from the [Visual Studio Marketplace](https://marketplace.visualstudio.com/items?itemName=github.vscode-codeql).
 
+To see what has changed in the last few versions of the extension, see the [Changelog](https://github.com/github/vscode-codeql/blob/master/extensions/ql-vscode/CHANGELOG.md).
+
 ![CI status badge](https://github.com/github/vscode-codeql/workflows/Build%20Extension/badge.svg)
 
 ## Features

extensions/ql-vscode/README.md

@@ -7,6 +7,8 @@ This project is an extension for Visual Studio Code that adds rich language supp
 * Provides an easy way to run queries from the large, open source repository of [CodeQL security queries](https://github.com/Semmle/ql).
 * Adds IntelliSense to support you writing and editing your own CodeQL query and library files.
 
+To see what has changed in the last few versions of the extension, see the [Changelog](https://github.com/github/vscode-codeql/blob/master/extensions/ql-vscode/CHANGELOG.md).
+
 ## Quick start overview
 
 The information in this `README` file describes the quickest way to start using CodeQL.