Bundle the example configuration into the binary

[hizkifw]

Ideally, users who downloaded the binary releases should not have to refer to GitHub to grab an example configuration file. The example config should be embedded with the include_str! macro, and be accessible with a command-line flag, something like this:

./hoshinova --example-config > config.toml

[DaniruKun]

Another option would also be to just have it in a public gist, or even just as an .example file in the repository, that hoshinova can directly download with the http client.