Document configurations more

[wookayin]

Let's improve the documentations.

The wiki pages Basic Usage and Full configuration are the place for the configuration documentation, and it provides most of configurable things.

But since users may be confused on the syntax, or might want to see the live examples.
Users are encouraged to see default.conf, but there are few comments on it. It would be great if we provide a little explanation on each field -- documentation as a code (but detailed explanation in wiki).

Moreover, it'd be also great to add some common-case examples of greed.conf into the Basic Usage wiki page.