Update README.md

Author: kennymckormick

README.md

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 # PYSKL
 
+> Note: This repo is currently not maintained by the developer. Feel free to create forks and develop based on this piece of codes.
+
 [![PWC](https://img.shields.io/endpoint.svg?url=https://paperswithcode.com/badge/revisiting-skeleton-based-action-recognition/skeleton-based-action-recognition-on-ntu-rgbd)](https://paperswithcode.com/sota/skeleton-based-action-recognition-on-ntu-rgbd?p=revisiting-skeleton-based-action-recognition)
 [![PWC](https://img.shields.io/endpoint.svg?url=https://paperswithcode.com/badge/dg-stgcn-dynamic-spatial-temporal-modeling/skeleton-based-action-recognition-on-ntu-rgbd-1)](https://paperswithcode.com/sota/skeleton-based-action-recognition-on-ntu-rgbd-1?p=dg-stgcn-dynamic-spatial-temporal-modeling)
 [![PWC](https://img.shields.io/endpoint.svg?url=https://paperswithcode.com/badge/revisiting-skeleton-based-action-recognition/skeleton-based-action-recognition-on-kinetics)](https://paperswithcode.com/sota/skeleton-based-action-recognition-on-kinetics?p=revisiting-skeleton-based-action-recognition)