add competition

Author: likyoo

COMPETITIONS.md

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+# Change Detection Competitions with cdp
+
+`change_detection.pytorch` has competitiveness and potential in the change detection competitions.
+Here you can find competitions, names of the winners and links to their solutions.
+
+
+
+------
+
+
+
+### [PRCV2021 Change Detection Competition](https://captain-whu.github.io/PRCV2021_RS/index.html)
+
+- 3rd place. 
+
+  [Kaiyu Li](https://github.com/likyoo), 
+  [Fulin Sun](https://github.com/LinoSun), 
+  Xudong Liu, 
+  Guoqiang Liu,  
+  [[description](https://github.com/likyoo/PRCV2021_ChangeDetection_Top3)]