feat: `/help` command

[sudojunior]

This intends to be a long-term enhancement, uncommon knowledge about the framework and it's nuances can be documented here - similar to how docs site has guides. The recent inclusion of Select Menus in modals serves to be a good example.

Given the structure of an FAQ, autocomplete would serve better over a series of choices.

https://github.com/sudojunior/hack-n-slash/blob/d1f6c876551de09727465ef39e7cc7b9529fc47d/src/commands/about.ts#L26-L34

Current structure of Hack 'n Slash's /about command, but it could be structured better.

Close ties with #6 and #7