add README

README.md

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+## About
+
+Adaption of the Jekyll version of [contrast](https://github.com/niklasbuschmann/contrast).
+
+## Features
+
+ - supports dark mode on macOS Mojave
+ - MathJax support
+ - no external ressources
+ - responsive
+
+## Based on
+
+- [Minima](https://github.com/jekyll/minima)
+- [KaTeX](https://katex.org/)
+
+## License
+
+[public domain](http://unlicense.org/)