Clarify how to use options in README

[KristerV]

I spent a good hour looking at source and issues before I figured out how to use and what options are available with what values exactly.

[coveralls]

Pull Request Test Coverage Report for Build 292

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 89.423%

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Totals
Change from base Build 236:	0.0%
Covered Lines:	186
Relevant Lines:	208

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💛 - Coveralls