安装报错

小白提问，装picky在zhanbin.appspot.com出错

Traceback (most recent call last):
File "/base/python_runtime/python_lib/versions/1/google/appengine/ext/webapp/__init__.py", line 511, in __call__
handler.get(*groups)
File "/base/data/home/apps/zhanbin/1.344259933651252454/main.py", line 52, in get
template_values['articles_total'] = articles.count()
File "/base/python_runtime/python_lib/versions/1/google/appengine/ext/db/__init__.py", line 1818, in count
result = raw_query.Count(limit=limit, rpc=rpc)
File "/base/python_runtime/python_lib/versions/1/google/appengine/api/datastore.py", line 1275, in Count
iterator = self._Run(limit=0, offset=offset, **kwargs)
File "/base/python_runtime/python_lib/versions/1/google/appengine/api/datastore.py", line 1188, in _Run
str(exc) + '\nThis query needs this index:\n' + yaml)
NeedIndexError: The index for this query is not ready to serve. See the Datastore Indexes page in the Admin Console.
This query needs this index:
- kind: Article
properties:
- name: is_page
- name: created
direction: desc