docs(overlays): fix overlays description

docs/plugins/overlays.md

@@ -17,7 +17,7 @@ To get list of visible data overlays, plugins can use the `getVisibleDataOverlay
 ##### Example of getVisibleDataOverlays usage:
 
 ```javascript
-window.minerva.overlays.data.getDataOverlays();
+window.minerva.overlays.data.getVisibleDataOverlays();
 ```
 
 #### Show an overlay
@@ -57,7 +57,10 @@ To add an overlay, plugins can use the `addDataOverlay` method defined in `windo
 ##### Example of addDataOverlay usage:
 
 ```javascript
-window.minerva.overlays.addDataOverlay(109);
+window.minerva.overlays.addDataOverlay({
+  name: 'Plugin Test',
+  fileContent: 'plugin test content',
+});
 ```
 
 #### Remove an overlay