README: add note about the layer license

Point to COPYING.MIT as the layer license.

Signed-off-by: Ricardo Salveti <[email protected]>

README.md

@@ -52,3 +52,7 @@ Branch **kirkstone** is not open for direct contributions, please raise an issue
 * Sourabh Banerjee <[email protected]>
 * Viswanath Kraleti <[email protected]>
 * Ricardo Salveti <[email protected]>
+
+## License
+
+This layer is licensed under the MIT license. Check out [COPYING.MIT](COPYING.MIT) for more detais.