Bug#976763: gdl: missing Homepage

[Rebecca N. Palmer]

That's the upstream source repository, not rendered documentation, but 
there doesn't seem to be anything better (the 
http://developer.gnome.org/gdl/ suggested in the documentation does not 
exist; I have reported this as 
https://gitlab.gnome.org/GNOME/gdl/-/issues/11 ) and it is common to use 
the repository URL in this case (about half of *all* Debian's Homepage 
fields point to https://github.com/...).