add MIT license

Author: amintimany

LICENSE

@@ -0,0 +1,9 @@
+MIT License
+
+Copyright (c) Iris Tutorial developers 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 in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

@@ -145,7 +145,10 @@ The hope is that the maintenance and extension of this tutorial becomes a collab
 
 If you have suggestions for future topics or improvements for existing ones, please add them to [TODO.md](TODO.md).
 
+**Note**: by contributing to the Iris Tutorial you agree that your contributions will be released under the terms of Iris Tutorial's license — see [the LICENSE file](LICENSE).
+
 ### How to Contribute
+
 To contribute, we recommend following these steps:
 
 1. Fork the repository.