Document 1.20.5 `hover:show_item` format

[bluelhf]

Adventure v4.26.1 introduced a new format for the show_item hover action to support the new 1.20.5 data components. Since this is already included in Paper 1.21.11 for example, it would be good to document it.

In v4.26.1, the following formats for show_item are supported:

1. <hover:show_item:(namespaced key)>, as in <hover:show_item:dirt>
2. <hover:show_item:(namespaced key):(item amount)>, as in <hover:show_item:dirt:5>
3. <hover:show_item:(namespaced key):(item amount):(snbt compound tag)>
   • Example: <hover:show_item:'minecraft:stone':6,'{display:{Name:{"text": "Hello from Stone!"}}}'>
   • The compound tag will be the value of the item's tag key as documented on minecraft.wiki.
   • This format will no longer be supported in Adventure v5.
4. <hover:show_item:(namespaced key):(item amount):(data component key 1):(data component value 1):(data component key 2):(data component value 2):(any number of other key-value pairs)>
   • Example: <hover:show_item:'minecraft:dirt':5:custom_name:'{"text":"Hello!"}':lore:'[{"text":"foo!"}]'>
   • This will completely replace the old SNBT format in Adventure v5.