Add doc.

src/hooks/useCookie.ts

@@ -4,7 +4,7 @@ import { useCallback, useEffect, useState } from 'react';
 /**
  * Custom hook that return csrf cookie fetched from server.
  *
- * @return cookie
+ * @return {string} cookie.
  */
 export const useCookie = (): string => {
   const [cookie, setCookie] = useState('');