add text clarifying when buttons can be used. Fixes microsoft#138204

Author: TylerLeonhardt

src/vscode-dts/vscode.d.ts

@@ -1675,7 +1675,9 @@ declare module 'vscode' {
 
 		/**
 		 * Optional buttons that will be rendered on this particular item. These buttons will trigger
-		 * an {@link QuickPickItemButtonEvent} when clicked.
+		 * an {@link QuickPickItemButtonEvent} when clicked. Buttons are only rendered when using a quickpick
+		 * created by the {@link window.createQuickPick()} API. Buttons are not rendered when using
+		 * the {@link window.showQuickPick()} API.
 		 */
 		buttons?: readonly QuickInputButton[];
 	}