add synthesis tool

doc/doc_ch/data_synthesis.md

-## 数据合成工具
+# 数据合成工具
 除了开源数据，用户还可使用合成工具自行合成。这里整理了常用的数据合成工具，持续更新中，欢迎各位小伙伴贡献工具～
 - [text_renderer](https://github.com/Sanster/text_renderer)
 - [SynthText](https://github.com/ankush-me/SynthText)
@@ -6,3 +6,4 @@
 - [TextRecognitionDataGenerator](https://github.com/Belval/TextRecognitionDataGenerator)
 - [SynthText3D](https://github.com/MhLiao/SynthText3D)
 - [UnrealText](https://github.com/Jyouhou/UnrealText/)
+- [SynthTIGER](https://github.com/clovaai/synthtiger)
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doc/doc_en/data_synthesis_en.md

@@ -9,3 +9,4 @@ There are the commonly used data synthesis tools, which will be continuously upd
 * [TextRecognitionDataGenerator](https://github.com/Belval/TextRecognitionDataGenerator)
 * [SynthText3D](https://github.com/MhLiao/SynthText3D)
 * [UnrealText](https://github.com/Jyouhou/UnrealText/)
+* [SynthTIGER](https://github.com/clovaai/synthtiger)
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