[DOC] update AUTHORS.rst file (#147)

The authors file still had 2018 content in it, this has been updated to
reflect the current status.

AUTHORS.rst

@@ -2,16 +2,10 @@
 Developers
 ==========
 
-**skpro** is developed open source under the direction of `Dr Franz Király`_. Check out the `public code repository`_ to learn more.
+**skpro** is developed by the sktime community.
 
-**Active contributors**
+We follow the all-contributors specification for giving credit.
+Contributions of any kind are welcome!
 
-* Franz Kiraly <f.kiraly@ucl.ac.uk> [`@fkiraly <https://github.com/fkiraly>`_]: project manager and designated point of contact
-* Frithjof Gressmann [`@frthjf <https://github.com/frthjf>`_]: principal developer and curator
-* Vitaly Davydov [`@iwitaly <https://github.com/iwitaly>`_]: contributor
-
-
-If you like to contribute, read our `contribution guide <https://github.com/sktime/skpro/CONTRIBUTING.md>`_.
-
-.. _public code repository: https://github.com/sktime/skpro
-.. _Dr Franz Király: https://www.ucl.ac.uk/statistics/people/franz-kiraly
+For a list of contributors, see the file
+`all-contributorsrc <https://github.com/sktime/skpro/blob/main/.all-contributorsrc>`_.