Can't find doc package for libappindicator

I am trying to make a simple indicator (a simple bar to show current brightness of screen) for my system tray with appindicator3. The problem is that none of the two tutorials that I found on the subject cover it, and I can't find any documentation about appindicator3. This issue has already been detected in the comments of this answer.

I thought my search had ended when I found libappindicator-doc and installed it,

apt-get install libappindicator-doc

However, there is nothing useful under /usr/share/doc/libappindicator-doc, just a changelog and a copyright.

Did I look in the wrong place? Never before have I found a useless /usr/share/doc/package-doc directory once installed the package-doc.