Update and rename LICENSE to LICENSE.md

***NO_CI***

LICENSE.md

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2019 nanoFramework
+Copyright (c) .NET Foundation and Contributors
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal