doc: refine the structure of data in and data out

docs/en/08-data-in/index.md

+---
+sidebar_label: Data In
+sidebar_title: How to Write Data Into TDengine Cloud Service
+---
+
+This chapter introduces a number of ways which can be used to write data into TDengine, users can use 3rd party tools, like telegraf and prometheus, to write data into TDengine cloud service, or use taosBenchmark(../../tools/taosbenchmark) which is a tool provided by TDengine to write data into TDengine cloud service. Furthermode, users can use taosX, which is also a tool provided by TDengine, to sync data from one TDengine cloud service to another.
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docs/en/09-data-out/index.md

+---
+sidebar_label: Data Out
+sidebar_title: How to Get Data Out of TDengine
+---
+
+This chapter introduces how to get data out of TDengine cloud service. Besides normal query using SQL, users can use data subscription which is provided by the message queue component inside TDengine to access the data stored in TDengine. `taosdump`, which is a tool provided by TDengine, can be used to dump the data stored in TDengine cloud service into files. `taosX`, which is another tool provided by TDengine, can be used to sync up the data in one TDengine cloud service into another.
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