Example configuration with Onionspray defaults

Description

It would be helpful for users if a canonical example configuration file had all/only Onionspray defaults.

Tasks

• Create a default.tconf with just the default configuration, and explanatory comments. Explain in the example.tconf that it's an example that does not necessariliy has the default parameters. Or just rename the example.tconf to default.tconf. Or something like that.
• Or just point to lib/do-configure.pl, where defaults are defined.
• Update the documentation accordingly, including:
  • "Configuration options" section in the usage guide (using.md).

Time estimation

• Complexity: negligible (0.1 day)
• Uncertainty: low (x1.1)
• Reference (adapted)