Readme.md

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This repository is for storing the binary files for Apache IoTDB project's document, compiler etc..

For example, if you have a figure in `docs/UserGuide/IoTDB-Introduction/What-is-IoTDB.md` in Apache IoTDB's repository, 
then please create a folder `docs/UserGuide/IoTDB-Introduction/What-is-IoTDB` in this repository, put the figure into 
the folder, and naming a meaningful figure name to the figure.

Exception: if the markdown file name is `readme.md`, then you do not need to add new folder anymore. 
For example, if you want to add figures to `docs/Download/readme.md`, then you just need to create a folder `docs/Download`,
and put all figures to the folder.

If you need to upload figure to some module's readme.md (For example, you want to add a figure into `tsfile/readme.md`,
you have to obey the similar rule: create a folder `tsfile`, and put all figures there.