Update the docs to reflect features that were added to Click

[janluke]

Relevant issues:

• Click 8.4.0 implements Did you mean <cmd>? suggestions: conside removing it from Cloup #199
• Arguments page describes a Click limitation that 8.5.0 removed #209
• Click has added type annotation, though they might still be less detailed/precise than Cloup ones (check on that)

Notable points to update:

• the readme
• the doc pages where features now available in Click are described: use a Sphinx admonition somewhere at the top where you mention the feature is now also in click >= {version}.

Note that cloup might implement some features regardless the version of click. And there might be small differences between cloup and click implementations.