Slash Commands (as per the new addition, if possible currently)

[alextecplayz]

Is your feature request related to a problem? Please describe.
It is not necessarily a problem, but it is wanted.

Describe the solution you'd like
A new category under the Command Handler tab with these new commands.

Describe alternatives you've considered
Haven't considered any alternatives yet other than the current command capabilities of Discord.JS

Additional notes
As per these two links:
Reddit - We can now make custom slash commands using bots!! discordapp
Discord Developer Portal - Documentation - Slash Commands

[tipakA]

The feature itself isn't even added to library yet, so there is currently nothing to write guide about.

The PR for the feature is at discord.js#5106, and there is no ETA on where it's going to be merged and/or released.

[almostSouji]

#638 takes care of this (new implementation!) and will be merged once we completed and archived the v12 guide