message: Add crates.io, docs.rs, and travis badges to readme
diff: # glfw-rs
  +[![Crates.io](https://meritbadge.herokuapp.com/glfw)](https://crates.io/crates/glfw)
  +[![Docs.rs](https://docs.rs/glfw/badge.svg)](https://docs.rs/glfw)
  +[![Build Status](https://travis-ci.org/PistonDevelopers/glfw-rs.svg?branch=master)](https://travis-ci.org/PistonDevelopers/glfw-rs)
  +
  GLFW bindings and wrapper for The Rust Programming Language.
  ## Example
  