feat(minimessage): Add info about requiring namespace for custom textures in paths

[Andre601]

Textures that are added to an atlas from a different namespace require you to add said namespace to the Sprite path to actually show.

Example: Assume a texture called ruby.png exists in assets/example/textures/item/ and is loaded by the items Atlas (due to it collecting everything under item/ directory).
The correct way to display the sprite now is <sprite:items:"example:item/ruby">

This PR updates the docs on the sprite tag to not only mention that, but also that the sprite name to use depends on the atlas, as it may or may not add a prefix for the path to use.

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[olijeffers0n]

Suggested change

	* `sprite` the sprite to use, e.g. `item/emerald`. Name is based on the atlas used, may or may not have a prefix (e.g. `item/` for items atlas) and may require a namespace, if the texture is not stored in the `minecraft` namespace (e.g. texture paths from `assets/example/textures/item/` require `example:` as namespace).
	* `sprite` the sprite to use, e.g. `item/emerald`. The name is based on the atlas used. It may have a prefix (e.g. `item/` for items atlas). If the texture is not stored in the `minecraft` namespace it may also require a namespace (e.g. texture paths from `assets/example/textures/item/` require `example:` as namespace).

Feel like this is a bit wordy