Update DescribeSubnet (#46)

Author: yufeiminds

docs/services.rst

@@ -101,3 +101,10 @@ UHub
 .. autoclass:: ucloud.services.uhub.client.UHubClient
    :members:
 
+
+VPC
+---
+
+.. autoclass:: ucloud.services.vpc.client.VPCClient
+   :members:
+

ucloud/client.py

@@ -119,3 +119,10 @@ def uhub(self):
         return UHubClient(
             self._config, self.transport, self.middleware, self.logger
         )
+
+    def vpc(self):
+        from ucloud.services.vpc.client import VPCClient
+
+        return VPCClient(
+            self._config, self.transport, self.middleware, self.logger
+        )