Add note about archiving the project

Author: sybrenstuvel

README.md

@@ -1,3 +1,29 @@
+# Python-RSA has been archived
+
+Hi folks,
+
+I'm Sybren, one of the original authors and the maintainer of this project.
+Unfortunately I don't have the time and brain space left to properly maintain
+Python-RSA. As you can see from the lack of activity on the open issues, and the
+lack of commits, that has been the case for a while now.
+
+As Python-RSA is included as a dependency in quite a few high-profile projects,
+I don't feel comfortable handing over the project to someone else. It's just too
+big of a risk.
+
+Thanks for having used this little library for so long, and in so many projects.
+I truely didn't expect that when I started working on it. Also big thanks to all
+the people helping out and improving the project.
+
+So that's it. If you want to keep the project alive, please fork it. Give it the
+love it deserves.
+
+Cheers,
+Sybren
+
+
+---------------------------------------------
+
 # Pure Python RSA implementation
 
 [![PyPI](https://img.shields.io/pypi/v/rsa.svg)](https://pypi.org/project/rsa/)