Improve cgit repository descriptions
"Unnamed repository; edit this file 'description' to name the repository." is not helpful. At least "Mirror of https://gitlab.alpinelinux.org/alpine" should be copied from top-level description, and preferably the actual repo should be shown, e.g. "Mirror of https://gitlab.alpinelinux.org/alpine/aports" under https://git.alpinelinux.org/aports.
Since no new cgit repos should be created, this can be done manually.