Extend help output with short overview

[wojas]

What does this PR change? What problem does it solve?

The list of subcommands can be confusing for first time users. This adds a short overview of the most important commands to help new users get started.

Was the change discussed in an issue or in the forum before?

No.

Checklist

• [x] I have read the Contribution Guidelines
• [x] I have enabled maintainer edits for this PR
• [ ] I have added tests for all changes in this PR
• [ ] I have added documentation for the changes (in the manual)
• [x] There's a new file in changelog/unreleased/ that describes the changes for our users (template here)
• [x] I have run gofmt on the code in all commits
• [x] All commit messages are formatted in the same style as the other commits in the repo
• [x] I'm done, this Pull Request is ready for review

[rawtaz]

We discussed this a bit and while it's a good idea, we think it's better to put the examples in a Quickstart or Getting started section in the documentation, and referring to that in the CLI help.

The main reasons are that the inline help becomes too long for a user running the help command in order to see the commands and options, as well as it being too incomplete for another user who's rather in need of more guidance material.

So it doesn't really match either of them, as it stands now, and thereby it's better to split it up like I mentioned above.