docs: update maintenance.md

Author: MichaelCurrin

docs/development/advanced/maintenance.md

@@ -1,4 +1,6 @@
-# Maintenance ntoes
+# Maintenance
+
+## Dependencies
 
 When upgrading `@types/vscode` in [package.json](/package.json), you must also upgrade the `engines.vscode` value manually.
 
@@ -9,3 +11,12 @@ ERROR  @types/vscode ^1.53.0 greater than engines.vscode ^1.52.0. Consider upgra
 ```
 
 Running the `test` command will not tell you about the error.
+
+
+## Images
+
+The extension icon listed in `package.json` must not be an SVG because of security limitations by VS Code. A PNG works fine.
+
+SVGs are used for "commands" though, for the extension's button.
+
+See [images](/images/).