Improved installation docs

Description

Installation docs needs improvements and cleansing.

Tasks

• Update the installation docs, including:
  • Needs to ensure Onionspray starts at boot, in three approaches:
    • Cron approach, using a /etc/cron.daily/onionspray-service file.
    • Trying with the command line.
    • Setting up a Systemd service, like in the Onionspray role.
  • Log rotation (so it does not fill the disk).

Time estimation

• Complexity: very small (0.5 day)
• Uncertainty: low (x1.1)
• Reference (adapted)