(Related to Wikimedia community discussions in http://fab.wmflabs.org/T271 )
1. Click on the "Upload file" icon in a Maniphest task.
2. Message says "To add files, drag and drop them into the comment text area."
Might not have an application to drag and drop from; might not run a platform supporting input interpreted as dragging. => Alternative ways of file uploading aren't discoverable from the UI.
* Mention that you can paste an image from the clipboard into the comment area.
* Link to /file/upload/ for classic upload (though it's rather unclear after uploading a file how to actually link to it from a Maniphest task)