docs: Add a blurb on the summary file
docs: Add a blurb on the summary file

We expect people to use it now, so let's actually describe what it is.

gatispaeglis/ostree,GNOME/ostree,gatispaeglis/ostree,GNOME/ostree,gatispaeglis/ostree,GNOME/ostree,GNOME/ostree,gatispaeglis/ostree,gatispaeglis/ostree,GNOME/ostree,gatispaeglis/ostree