docs: add detailed usage instructions and example for the unload command

Author: NonSwag

content/docs/worlds/manage/unload.mdx

@@ -2,3 +2,13 @@
 title: Unload a world
 description: How to use the world unload command.
 ---
+
+You can unload worlds with the `/world unload <world> [<fallback>]` command.  
+The fallback option allows you to specify a world to send players to, if they are currently in the world that is being unloaded.  
+If undefined, players will be sent to the default world (usually `minecraft:overworld`).
+
+## Example
+
+```
+/world unload worlds:my_world worlds:my_fallback_world
+```