Add the latest docs badge to README.md (#128)

README.md

@@ -4,6 +4,7 @@ LsqFit.jl
 The LsqFit package is a small library that provides basic least-squares fitting in pure Julia under an MIT license. The basic functionality was originaly in [Optim.jl](https://github.com/JuliaNLSolvers/Optim.jl), before being separated into this library.  At this time, `LsqFit` only utilizes the Levenberg-Marquardt algorithm for non-linear fitting.
 
 [![Build Status](https://travis-ci.org/JuliaNLSolvers/LsqFit.jl.svg)](https://travis-ci.org/JuliaNLSolvers/LsqFit.jl)
+[![latest](https://img.shields.io/badge/docs-latest-blue.svg)](https://julianlsolvers.github.io/LsqFit.jl/latest/)
 
 [![LsqFit](http://pkg.julialang.org/badges/LsqFit_0.3.svg)](http://pkg.julialang.org/?pkg=LsqFit&ver=0.3)
 [![LsqFit](http://pkg.julialang.org/badges/LsqFit_0.4.svg)](http://pkg.julialang.org/?pkg=LsqFit&ver=0.4)