Searching for the layer-apt documentation took me along this path:
Juju docs for layers > Juju layer index > Layer Apt LP repo > Layer-apt master branch > Layer Apt master branch tree > layer-apt README.md.
The resulting view is unparsed MD. I guess this is auto-mirrored from Github or vice/versa?
Carrying on, at the bottom of the unparsed readme are several links, which aren’t parsed so not clickable. One looks promising: https://answers.launchpad.net/layer-apt. Switch to the overview tab > https://launchpad.net/layer-apt. Hey, there’s a link to a Github repo > https://github.com/stub42/layer-apt. Result! A nice formatted readme file for charm authors looking to understand layer-apt is a mere 9 clicks away
I suggest perhaps linking to the gh repo from the layer index?