gmessages: Document namespacing recommendation for structured log fields
gmessages: Document namespacing recommendation for structured log fields

We recommend that all custom log fields are namespaced to avoid
collisions.

https://bugzilla.gnome.org/show_bug.cgi?id=744456

endlessm/glib,johne53/MB3Glib,endlessm/glib,endlessm/glib,johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib,endlessm/glib,endlessm/glib