document required extensions in readme

Author: bcpeinhardt

README.md

@@ -13,6 +13,10 @@ The Coder Remote extension lets you open
 - Works in air-gapped or restricted networks. Just connect to your Coder
   deployment!
 - Supports multiple editors: VS Code, Cursor, and Windsurf.
+  > [!NOTE]  
+  > The extension builds on VSCode provided implementations of SSH. Make sure you have
+  > the correct ssh extension installed for your editor (ms-vscode-remote.remote-ssh or 
+  > codeium.windsurf-remote-openssh for windsurf)
 
 ![Demo](https://github.com/coder/vscode-coder/raw/main/demo.gif?raw=true)