Write release notes to be informative

[yoichitgy]

Release notes are important for users to understand updates and pick a version to use. The notes should be more informative.

Examples:
https://github.com/Swinject/Swinject/releases
https://github.com/realm/SwiftLint/releases
https://github.com/ikesyo/Himotoki/releases

@Lutzifer you can pick any style as you like😉