hotfix: include readthedocs from original repo

Author: simonprovost

README.rst

@@ -6,6 +6,9 @@ Deep Forest (DF) 21 (Support for Python 3.10+)
 .. |github| image:: https://github.com/simonprovost/deep_forest_py310/workflows/DeepForest-CI/badge.svg
 .. _github: https://github.com/LAMDA-NJU/Deep-Forest/actions
 
+.. |readthedocs| image:: https://readthedocs.org/projects/deep-forest/badge/?version=latest
+.. _readthedocs: https://deep-forest.readthedocs.io/en/latest/
+
 .. |codecov| image:: https://codecov.io/gh/LAMDA-NJU/Deep-Forest/branch/master/graph/badge.svg?token=5BVXOT8RPO
 .. _codecov: https://codecov.io/gh/LAMDA-NJU/Deep-Forest