* [ui] add method to import file to doc editor.

lib/zin/wg/docapp/js/v1.js

@@ -578,6 +578,19 @@ function renameDocFile(file, doc)
     });
 }
 
+/* Import markdown or json file to editor. */
+function importFileToEditor(type)
+{
+    const accept = type === 'markdown' ? '.md' : '.json';
+    return zui.selectFile(accept).then(file => {
+        if(!file) return;
+        zui.readFile(file).then(content => {
+            if(typeof content !== 'string' || !content.length) return;
+            return getDocApp().importDoc(content, type, file.name.split('.').shift());
+        });
+    });
+}
+
 /**
  * 定义文档各个试图和 UI 元素的上的操作方法。
  * Define the operation methods on the views and UI elements of the doc.