Fix bug on code CKEditor component example (strapi#209)

Without this prop, the content of the text editor will load empty when accessing a content entry on Strapi admin.
This ensures that the data is correctly initialized on CKEditor

Co-authored-by: Pierre Wizla <[email protected]>

docs/developer-docs/latest/guides/registering-a-field-in-admin.md

@@ -363,6 +363,7 @@ const Editor = ({ onChange, name, value }) => {
         editor={ClassicEditor}
         config={configuration}
         data={value}
+        onReady={editor => editor.setData(value)}
         onChange={(event, editor) => {
           const data = editor.getData();
           onChange({ target: { name, value: data } });