Fix lint complaints coming up from GitHub actions by having more complete examples in the docs.

docs/source/developer/virtualdom.create.tsx

@@ -8,3 +8,4 @@ function MyComponent() {
 }
 
 const myWidget: Widget = ReactWidget.create(<MyComponent />);
+Widget.attach(myWidget, document.body);

docs/source/developer/virtualdom.reactwidget.tsx

@@ -12,3 +12,4 @@ class MyWidget extends ReactWidget {
   }
 }
 const myWidget: Widget = new MyWidget();
+Widget.attach(myWidget, document.body);

docs/source/developer/virtualdom.usesignal.tsx

@@ -23,3 +23,4 @@ class MyWidget extends ReactWidget {
 }
 
 const myWidget: Widget = new MyWidget();
+Widget.attach(myWidget, document.body);