Update content of managing emojis in directory

[germainelee]

As Admin Emojis page will be linking to this documentation, clarity is essential for users interested in uploading emoji pack owncast/owncast#4042

[gabek]

Sorry to be so pedantic. But that directory isn't just for bulk uploading. It's just for managing your custom emoji files in general. So maybe we could do something like

You can manage your custom emoji images in the data/emoji directory on your filesystem. You might want to do this for

• Adding multiple emoji files at once
• Deleting an entire set of emoji
• Renaming a custom emoji file
• Backing up your custom emoji or copying them elsewhere

[germainelee]

Thanks for pointing me in the right direction. I've revised the text.