Added write-ups on setting the editor content and refreshing the editor. Added link to font file

1. If you are self-hosting the Editor vs. linking to it, you additionally need the icon font file if you are using the toolbar. Added link
2. To set the content programmatically instead of picking up from text area, we can use editor.codemirror.setValue
3. If there are changes in sizes or hiding/unhiding of editor, we need to call editor.codemirror.refresh to make things look correct