Add usage docs to README

[nathanielks]

Hi there!

I'm interested in using this, but I'm not sure how. I cloned the repo and attempted to build from source to hopefully get some help text, but there's no Makefile in build/, either. Thanks for sharing this!

[kynetiv]

@nathanielks As far as building the tool, I found this to work:

cd build
cmake ../
make

[nathanielks]

Good on you, thanks for sharing @kynetiv !

[mmurasawa]

Perfect....! Thank you !!! @kynetiv !!!