[Brigadier] Quick reference

[Strokkur424]

[!NOTE] This issue is part of a series of issues regarding the extension of the Paper documentation regarding Paper's Brigadier API.

I feel like it'd be great for returning users to have a very simple and quick reference they can use to refresh their knowledge on certain aspects.

For example, there could be a section called "permission declaration" which quickly repeats that one can use the requires method to check the sender's permission in order to execute and view a command or argument.

Possible aspects referenced could be:

• Argument declaration
• Argument retrieval
• Permission declaration
• Difference sender and executor
• Custom argument suggestions
• Custom arguments
• Registering commands