Update .md files for SEO-ness

[thinkingserious]

We received an awesome PR for #hacktoberfest on our ruby library
We would love to see the same thing on the README in this repo as well.
Please replace the "-" with "_" in README, CONTRIBUTING, USE_CASES, USAGE files.

Thanks and happy Hacktoberfest!!

Submitted PR for diff. USE_CASES and USAGE .md files do not seem to exist in this repository. Also I replaced the "_" with the "-" as I believe that was the goal, similar to the ruby library.