Add CHANGELOG.md

[Raruto]

Restore changelog file for the next branch.

Related Issues:

• Versions
• Adding changelog
• Which cockpit version introduces webhook?
• Please add changelog and update docs
• How can the community support developing a better documentation?
• Upgrade 0.13.0 -> 0.5.5

---

Note for the readers

• see Remove changelog from the next branch #522 for latest available changelog of legacy branch
• see keepachangelog.com for generic guidelines
• see Raruto/cockpit/CHANGELOG.md for sample preview

---

Bonus tip:

The following markdown syntax allows an "automatic link generation" for getting a quick comparison between different cockpit releases.

## [Unreleased]

## [0.11.2] - 2020-09-14
## [0.11.1] - 2020-09-09
## [0.11.0] - 2020-07-25

...

[unreleased]: https://github.com/agentejo/cockpit/compare/0.11.2...HEAD

[0.11.2]: https://github.com/agentejo/cockpit/compare/0.11.1...0.11.2
[0.11.1]: https://github.com/agentejo/cockpit/compare/0.11.0...0.11.1
[0.11.0]: https://github.com/agentejo/cockpit/compare/0.10.2...0.11.0

NB the following file starts from version 0.11.0 only to demonstrate how the scheme works, anyone who wants to contribute further can start from checking the following link: 0.11.2...HEAD

[MarcoDaniels]

I've been wanting for a changelog.md for some time now. It would be really nice to have this merged and up to date. @aheinze what would be your take on it? Should we go though the commits and keep adding to this PR?

[aheinze]

@MarcoDaniels would be great! Any contribution is welcomed!

[remluben]

@aheinze ist there anything else to do in this? When are you going to merge this PR?