Add imageio

Author: almarklein

Diff for: _sections/30-projects.md

@@ -42,3 +42,4 @@ These projects pledge to drop Python 2 support in or before 2020.
 - [gala](https://gala.readthedocs.io)
 - [cual-id](https://github.com/johnchase/cual-id)
 - [CIS](https://github.com/cedadev/cis)
+- [imageio](https://imageio.github.io)