Add basic doc string to endpoint object (#25)

Author: justinGilmer

btrdb/endpoint.py

@@ -38,6 +38,8 @@
 
 
 class Endpoint(object):
+    """Server endpoint where we make specific requests."""
+
     def __init__(self, channel):
         self.stub = btrdb_pb2_grpc.BTrDBStub(channel)