v2.0.2

Fixed

• A single system with no sys in its config entry now gets a working jd
  command. The docs always said sys is only needed for more than one
  system, but the code silently skipped defining jd at all when it was
  missing, with no error. jd now falls back to the entry's position in
  the config.
• More than one system with an entry missing sys now prints an error at
  shell start, instead of silently leaving that system with no command.