README: mention license and contributing guide

Author: tarleb

LICENSE

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2017-2020 John MacFarlane and contributors
+Copyright (c) 2017-2020 pandoc Lua filters 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

README.md

@@ -1,8 +1,8 @@
-[![travis build
-status](https://img.shields.io/travis/pandoc/lua-filters/master.svg?label=travis+build)](https://travis-ci.org/pandoc/lua-filters)
-
 # Lua Filters
 
+[![Travis build status][Travis badge]](https://travis-ci.org/pandoc/lua-filters)
+[Travis badge]: https://img.shields.io/travis/pandoc/lua-filters/master.svg?label=travis+build
+
 This repository collects Lua filters for pandoc.
 
 To learn about Lua filters, see the
@@ -33,8 +33,13 @@ requirements.
 Contributing
 ------------
 
-PRs for new filters are welcome, provided they conform to these
-guidelines. Lua code should ideally follow the Olivine Labs [Lua
-style guide].
+PRs for improvements, bug fixes, or new filters are welcome.
+Please see CONTRIBUTING.md for additional information.
+
+License
+-------
+
+All filters are published under the MIT license by their
+respective authors. See LICENSE for details.
 
 [Lua style guide]: https://github.com/Olivine-Labs/lua-style-guide