improve documentation: add configuration examples

[adamjanicki2]

Part of #33

This PR contains a few simple examples of how to configure Treecle with custom configs. A follow-up PR will handle all usage examples

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[LeaVerou]

I think the examples section should have usage examples, not configuration examples. The defaults should already work with a good variety of trees. You could then have a section on Configuration lower down.

[adamjanicki2]

I think the examples section should have usage examples, not configuration examples. The defaults should already work with a good variety of trees. You could then have a section on Configuration lower down.

Got it; I'll move these down into a separate configuration section, and then make a follow-up PR to add the usage examples section so then this PR isn't massive. Does that sound ok with you @LeaVerou ?