Documentation: add more comments

[mahal]

Description

The package is lacking some substantial documentation. Keyboard is quite powerful but the documentation doesn't reflect it. It was quite irritating for me at the beginning on what to do with the Keyboard, how to use and interact with it.

Proposed Solution

Add comments to structs, attributes, classes and funcs so docc can generate more detailed documentation.

Describe Alternatives You've Considered

More examples in Cookbook for Keyboard, like MIDI-Monitoring, touch location for velocity, using latching keyboard,programmatically unpressing keys, reading pressed keys to describe the tonic, ...

Additional Context

Does the multitouch bug still exist? if yes, i've been hunting it as well before reading in the repo. Might also briefly explain it in the doc. It's quite irritating that some interaction is possible in touch down and other not. https://github.com/AudioKit/AppleBugDemos/tree/main#swiftuigesturesblockuikittouches

[mahal]

Created Pull request #28 as a starting point, this is nowhere complete and I would like to invite others who have more experience with Keyboard for support and PRs.

[aure]

Sorry for the delay in accepting your pull request, it got lost in my mailbox.