Make user documentation more accessible

[straight-shoota]

The CLI provides documentation for rules and the API docs provide some information as well. That's good, but not very approachable.
Users of ameba should not need to dig through the developer documentation. And reading documentation on the command line can be useful, but it's limited.

It would be a good improvement to have explicit user documentation. The best place for this would probably be the website (https://crystal-ameba.github.io/).

The main components would be basic usage instructions, expands on what's currently in README.
And documentation for the individual rules. This in particular is important and currently not very approachable within the API docs.
The contents could be automatically synced with doc comments in the sources.

[Sija]

Both the API and CLI docs are covering rules' descriptions along with examples and available options. I agree that the API docs are more technical, since they're based on the standard Crystal docs output, yet that's sth one cannot say about the ones provided through the CLI.

I'm most likely biased due to the overall familiarity with the project, so could you please explain in more detail what exactly do you find missing?

[straight-shoota]

I'd like to have user-facing documentation somewhere on the web. Similar to what the CLI offers, but linkable and accessible without having ameba installed. And without the noise of the developer-focused API docs.

A simple way to implement that would be to put the API doc comments from the sources into Markdown files in https://github.com/crystal-ameba/crystal-ameba.github.io