Update README.md

Since Cocoapods is supported, how about adding the pod badge to the readme?

-#Masonry [![Build Status](https://travis-ci.org/SnapKit/Masonry.svg?branch=master)](https://travis-ci.org/SnapKit/Masonry) [![Coverage Status](https://img.shields.io/coveralls/SnapKit/Masonry.svg?style=flat-square)](https://coveralls.io/r/SnapKit/Masonry) [![Carthage compatible](https://img.shields.io/badge/Carthage-compatible-4BC51D.svg?style=flat)](https://github.com/Carthage/Carthage)
+#Masonry [![Build Status](https://travis-ci.org/SnapKit/Masonry.svg?branch=master)](https://travis-ci.org/SnapKit/Masonry) [![Coverage Status](https://img.shields.io/coveralls/SnapKit/Masonry.svg?style=flat-square)](https://coveralls.io/r/SnapKit/Masonry) [![Carthage compatible](https://img.shields.io/badge/Carthage-compatible-4BC51D.svg?style=flat)](https://github.com/Carthage/Carthage) ![Pod Version](https://img.shields.io/cocoapods/v/Masonry.svg?style=flat)
 
 **Masonry is still actively maintained, we are committed to fixing bugs and merging good quality PRs from the wider community. However if you're using Swift in your project, we recommend using [SnapKit](https://github.com/SnapKit/SnapKit) as it provides better type safety with a simpler API.**