To add "unmaintained" warning

[baldram]

I see the proper warning on Github page (the README.md).
Unfortunately most users will try to install and use this plugin from the Grav Admin GUI.
Then it looks like below (no warning). I think some additional information might be added there.

PS: I fixed one bug.
Maybe this plugin can be still resurrected...?
Adobe says: "If you currently use the old Aviary SDK, please migrate to the new Creative SDK Image Editor".
https://www.adobe.io/apis/creativecloud/creativesdk/docs/websdk.html#/articles/gettingstarted/index.html
https://github.com/CreativeSDK/web-getting-started-samples

[matbrgz]

Start this project, it would be amazing.

[baldram]

Start this project, it would be amazing.

Please, go ahead! ;)