docs: clarify how to flush data at the end of script (#174)

* docs: clarify how to flush data at the end of script

* docs: added close() method to WriteApi

Author: bednar

README.rst

@@ -215,6 +215,8 @@ Writes
 The `WriteApi <https://github.com/influxdata/influxdb-client-python/blob/master/influxdb_client/client/write_api.py>`_ supports synchronous, asynchronous and batching writes into InfluxDB 2.0.
 The data should be passed as a `InfluxDB Line Protocol <https://docs.influxdata.com/influxdb/latest/write_protocols/line_protocol_tutorial/>`_\ , `Data Point <https://github.com/influxdata/influxdb-client-python/blob/master/influxdb_client/client/write/point.py>`_ or Observable stream.
 
+**Important: The WriteApi in batching mode (default mode) is suppose to run as a singleton. To flush all your data you should call ``_write_client.close()`` at the end of your script.**
+
 *The default instance of WriteApi use batching.*
 
 The data could be written as

influxdb_client/client/write_api.py

@@ -260,6 +260,10 @@ def flush(self):
         # TODO
         pass
 
+    def close(self):
+        """Flush data and dispose a batching buffer."""
+        self.__del__()
+
     def __del__(self):
         """Close WriteApi."""
         if self._subject: