add major features to readme

README.md

@@ -4,3 +4,20 @@ Open-MMLab Detection Toolbox
 **Note:** 
 
 We are still working on organizing the codebase. This toolbox will be formally released by the end of September. Stay tuned!
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+---
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+## Major Features
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+- **Modular Design**
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+  One can easily construct a customized object detection framework by combining different components. 
+  
+- **Support of multiple frameworks out of box**
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+  The toolbox directly supports popular detection frameworks, *e.g.* Faster RCNN, Mask RCNN, and R-FCN, etc.
+  
+- **State of the art**
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+  This was the codebase of the *MMDet* team, who won the [COCO Detection 2018 competition](http://cocodataset.org/#detection-leaderboard). 
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