Add deprecation notice for Python 3.5

Author: mhaas

CHANGELOG.md

@@ -29,6 +29,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 [#97]: https://github.com/SAP/data-attribute-recommendation-python-sdk/pull/97
 [#98]: https://github.com/SAP/data-attribute-recommendation-python-sdk/pull/98
 
+### Deprecated
+
+* Python 3.5 has reached [end-of-life in September 2020](https://www.python.org/downloads/release/python-3510/).
+  Support for Python 3.5 will be removed in one of the upcoming releases.
+
 
 ### Changed