Comment 1 for bug 1592388

index.json files have a field for descriptions, but we've never put anything interesting in there. See for example http://system-image.ubuntu.com/ubuntu-touch/devel/krillin.en/generic/index.json

I think it's always been the intent to put something useful there. Those fields are available through the D-Bus API so system-settings could display it. We even had an elaborate design for i18n'd descriptions but because those were never used and there were some open bugs about it, that feature pretty much just bitrotted.