Some updates to README.md

It's not 100% fine, yet… but at least it contains no lies :P
Create CONTRIBUTORS.md
Fix for comment by @hernanrivasacosta

[this comment](https://github.com/inaka/sumo_db/pull/85#discussion_r19343863)
Fix for comment by @HernanRivasAcosta

[this comment](https://github.com/inaka/sumo_db/pull/85#discussion_r19343991)
Fix for comment by @HernanRivasAcosta

[this comment](https://github.com/inaka/sumo_db/pull/85#discussion_r19344053)
a period
Merge pull request #85 from inaka/elbrujohalcon.updated.readme

README + CONTRIBUTORS