Add MIT-license button

Author: MartinOtter

LICENSE

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2017 ModiaSim
+Copyright (c) 2017-2018 ModiaSim developers
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

README.md

@@ -3,6 +3,7 @@
 [![Travis](https://travis-ci.org/ModiaSim/Modia.jl.svg?branch=master)](https://travis-ci.org/ModiaSim/Modia.jl)
 [![Coverage Status](https://coveralls.io/repos/github/ModiaSim/Modia.jl/badge.svg?branch=master)](https://coveralls.io/github/ModiaSim/Modia.jl?branch=master)
 [![codecov.io](http://codecov.io/github/ModiaSim/Modia.jl/coverage.svg?branch=master)](http://codecov.io/github/ModiaSim/Modia.jl?branch=master)
+[![The MIT License](https://img.shields.io/badge/license-MIT-brightgreen.svg?style=flat-square)](https://github.com/ModiaSim/Modia.jl/blob/master/LICENSE.md)
 
 ## Introduction