Add installation guide to VS Code Extension readme

vscode-extension/README.md

@@ -9,9 +9,16 @@ The Numbat extension provides language support for the [Numbat](https://github.c
 - comment toggling
 - autosurrounding brackets
 
+## Installation
+
+To install this extension you will need to download the extension installation file (VSIX file), which can be found in the assets of each [numbat release](https://github.com/sharkdp/numbat/releases) after v1.14.0.  
+Once the VSIX file has been downloaded, open visual studio code and go to the _Extensions_ tab of the sidebar. Click the three dots in the upper right corner of the tab and chose the _"Install from VSIX..."_ option. Find the VSIX file via the file picker and select it to install it.
+
+![Screenshot of an the open extensions menu with the "Install from VSIX..." option underlined in red](./assets/installation-instruction.png)
+
 ## Requirements
 
-_TO BE DONE_  
+_None_  
 
 ## Extension Settings