Added to docs: Setting the editor content and refreshing the editor

- If we need to set the content programmatically instead of picking up from text area, we can use `editor.codemirror.setValue()`. This is currently not mentioned in the documentation
- If there are changes in sizes or hiding/unhiding of editor (eg. using the editor in a modal dialog), the editor content does not show correctly. We need to call `editor.codemirror.refresh()` programmatically after the visibility/sizing is complete to make things look correctly. This is also documented in the [CodeMirror API documentation](http://codemirror.net/doc/manual.html#api_sizing)
3. If you are self-hosting the Editor vs. pulling it from the CDN, you additionally need the icon font file if you are using the toolbar. This is not clear in the documentation and added the link.