Add caveat to gsettings-destkop-schemas

> Is there a formula for that?

Here is an unfinished one. You will need to install pylast w/ pip.
https://gist.github.com/TingPing/826363c1ebc96cf8efd2

>Sounds like it maybe should be fixed in the application.

It is gstreamer that uses gio which looks for gsettings, nothing to do with the application.