[UpdateDoc]Update Doc for container_name

#618

Author: xiafu-msft

azure-storage-blob/azure/storage/blob/baseblobservice.py

@@ -653,6 +653,9 @@ def create_container(self, container_name, metadata=None,
 
         :param str container_name:
             Name of container to create.
+            The container name may only contain lowercase letters, numbers, and hyphens, and must begin with a letter or
+            a number. Each hyphen must be preceded and followed by a non-hyphen character. The name must also be
+            between 3 and 63 characters long.
         :param metadata:
             A dict with name_value pairs to associate with the
             container as metadata. Example:{'Category':'test'}