Extension link (#2736)

* Add links in docs

* Fix typo

* Add links of projects

* Add paper links

README.md

@@ -89,6 +89,7 @@ Other features
 - [x] [FSAF](configs/fsaf/README.md)
 - [x] [PAFPN](configs/pafpn/README.md)
 
+Some other methods are also supported in [projects using MMDetection](./docs/projects.md).
 
 ## Installation
 

docs/projects.md

+# Projects
+
+There are many projects built upon MMDetection.
+Some of them are published in top-tier conferences (CVPR, ICCV, and ECCV), the others are also highly influencial.
+We list some of them as examples of how to extend MMDetection for your own projects.
+Pull requests are also welcomed.
+
+To make this list also a reference for the community to develop and compare new object detection algorithms, we list them following the time order of top-tier conferences.
+Methods already supported and maintained by MMDetection are not listed.
+
+- [SEPC](https://github.com/jshilong/SEPC): [Scale-equalizing Pyramid Convolution for Object Detection](https://arxiv.org/abs/2005.03101), CVPR2020.
+- [TSD](https://github.com/Sense-X/TSD): [Revisiting the Sibling Head in Object Detector](https://arxiv.org/abs/2003.07540), CVPR2020.
+- [PolarMask](https://github.com/xieenze/PolarMask): [Single Shot Instance Segmentation with Polar Representation](https://arxiv.org/abs/1909.13226), CVPR2020.
+- [Hit-Detector](https://github.com/ggjy/HitDet.pytorch): [Hierarchical Trinity Architecture Search for Object Detection](https://arxiv.org/abs/2003.11818), CVPR2020.
+- [ZeroQ](https://github.com/amirgholami/ZeroQ): [A Novel Zero Shot Quantization Framework](https://arxiv.org/abs/2001.00281), CVPR2020.
+
+- [CBNet](https://github.com/VDIGPKU/CBNet): [A Novel Composite Backbone Network Architecture for Object Detection](https://aaai.org/Papers/AAAI/2020GB/AAAI-LiuY.1833.pdf), AAAI2020
+- [RDSNet](https://github.com/wangsr126/RDSNet): [A New Deep Architecture for Reciprocal Object Detection and Instance Segmentation](https://arxiv.org/abs/1912.05070), AAAI2020.
+- [TTFNet](https://github.com/ZJULearning/ttfnet): [Training-Time-Friendly Network for Real-Time Object Detection](https://arxiv.org/abs/1909.00700), AAAI2020.
+
+- [Cascade RPN](https://github.com/thangvubk/Cascade-RPN): [Delving into High-Quality Region Proposal Network with Adaptive Convolution](https://arxiv.org/abs/1909.06720), NeurIPS 2019.
+- [Reasoning R-CNN](https://github.com/chanyn/Reasoning-RCNN): [Unifying Adaptive Global Reasoning into Large-scale Object Detection](http://openaccess.thecvf.com/content_CVPR_2019/papers/Xu_Reasoning-RCNN_Unifying_Adaptive_Global_Reasoning_Into_Large-Scale_Object_Detection_CVPR_2019_paper.pdf), CVPR2019.
+- [DOTA](https://github.com/dingjiansw101/AerialDetection): [Learning RoI Transformer for Oriented Object Detection in Aerial Images](https://arxiv.org/abs/1812.00155), CVPR2019.
+
+- [SOLO](https://github.com/WXinlong/SOLO): [Segmenting Objects by Locations](https://arxiv.org/abs/1912.04488)
+- [SOLOv2](https://github.com/WXinlong/SOLO): [Dynamic, Faster and Stronger](https://arxiv.org/abs/2003.10152)
+- [Dense Peppoints](https://github.com/justimyhxu/Dense-RepPoints): [Representing Visual Objects with Dense Point Sets](https://arxiv.org/abs/1912.11473).
+- [IterDet](https://github.com/saic-vul/iterdet): [Iterative Scheme for Object Detection in Crowded Environments](https://arxiv.org/abs/2005.05708)
+- [CBN](https://github.com/Howal/Cross-iterationBatchNorm): [Cross-Iteration Batch Normalization](https://arxiv.org/abs/2002.05712)