create func to create markdown file from string

src/server/service/export.js

@@ -350,6 +350,16 @@ class ExportService {
     return zipFile;
   }
 
+  /**
+   * create markdown file from String
+   * @param {String} exportData String will write in file
+   * @param {String} fileName filename without extension
+   */
+  cretaeMarkdownFile(exportData, fileName) {
+    const filePath = path.join(this.baseDir, `${fileName}.md`);
+    fs.writeFile(filePath, exportData, (err) => {});
+  }
+
 }
 
 module.exports = ExportService;