add user admin to uucp group
add user admin to uucp group

- for
  - access to "rs-232 serial ports and devices connected to them"
  - consistency with voidvault
    - note
      - `uucp` group appears to be arch's equivalent to void's `dialout`
        group
- see
  - https://wiki.archlinux.org/index.php/users_and_groups#User_groups

atweiden/holovault