增加了公告的API接口和相应的API测试

announcement/serializers.py

@@ -0,0 +1,8 @@
+# coding=utf-8
+from rest_framework import serializers
+
+
+class AnnouncementSerializer(serializers.Serializer):
+    title = serializers.CharField(max_length=50)
+    description = serializers.CharField(max_length=10000)
+