https://github.com/benbalter/licensee, which is commonly used, also by
GitLab, to detect licenses have problems with detecting a proper
license, when additional text is added.

Because of this we've made a decision, that:

- LICENSE file will contain the plain text of the MIT license, having
  only the copyright years and owners as the custom change
- NOTICE file will contain additional info, that MIT license is applied
  only to our own software and that any other software included into
  this project is licensed under own license.