Readme: Clarify CONFIG_DIR and recommend copy of config template

[inkarkat]

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Documentation: Clarify that CONFIG_DIR is for the configuration template, not meant as the configuration to use

Add a Configuration section (between Installing and Usage) with overview and recommendation to copy the template.

Fixes #377

[inkarkat]

@karbassi Another user got confused here; could you please merge this really soon?! I haven't heard from you in a while; is everything alright? If you don't have any time for the project right now, I could merge my own pending PRs (and some other simple ones) to reduce the backlog.