Update systemd unit configuration file
Update systemd unit configuration file

Changes in detail:

 1. Change script name to `tldr_bot.py`.
 2. Add `Wants=` and `After=` directives to start the service after
    the network is online.
 3. Add recommended `User=` and `Group=` directives to run the
    as a specific user different than `root`.
 4. Reorder fields in order of importance.

tldr-pages/tldr-bot