Shields.io badge for latest rebar & pylon version

[ybw0014]

[![Latest Rebar](https://img.shields.io/github/v/release/pylonmc/rebar?style=flat-square)](https://github.com/pylonmc/rebar/releases/latest)
[![Latest Pylon](https://img.shields.io/github/v/release/pylonmc/pylon?style=flat-square)](https://github.com/pylonmc/pylon/releases/latest)

Might be useful on home page, how to install page.