feat: Document command restrictions (#610)

Author: Strokkur424

src/content/docs/paper/dev/api/command-api/basics/assets/custom-restriction.png

@@ -2,6 +2,7 @@
 title: Requirements
 description: A guide to setting requirements for commands.
 slug: paper/dev/command-api/basics/requirements
+version: 1.21.6
 ---
 
 Sometimes you want to limit a player's ability to use and/or view certain commands or subcommands. Exactly for this purpose,
@@ -70,7 +71,44 @@ Commands.literal("reloadcommands")
     });
 ```
 
-## Automating command reloads
+### Automating command reloads
 Forcing a player to reload their own commands is not a viable option for user experience. For this reason, you can **automate** this behavior. It is safe to call
 the update commands method as often as required, but it should generally be avoided as it can cost a great deal of bandwidth. If possible, you should instead place
 these in very specific spots. Furthermore, this method is completely thread safe, meaning you are free to call it from an asynchronous context.
+
+## Restricted commands
+From 1.21.6 onwards, commands can now be restricted. This feature is used by Vanilla in order to make a player confirm whether they
+really want to run a command from a run-command click event. That includes ones on text components or dialog buttons.
+All Vanilla commands, which require operator status by default, are restricted:
+
+![](./assets/vanilla-restriction.png)
+
+### Restricting your commands
+You can apply the same behavior to your commands by wrapping the predicate inside your `.requires` with `Commands.restricted(...)`.
+A simple implementation might look like this:
+
+```java
+Commands.literal("test-req")
+    .requires(Commands.restricted(source -> true))
+    .executes(ctx -> {
+        ctx.getSource().getSender().sendRichMessage("You passed!");
+        return Command.SINGLE_SUCCESS;
+    });
+```
+
+![](./assets/custom-restriction.png)
+
+<br />
+
+Inside the `.restricted` method you can put any logic which you would put into your `.requires` method.
+It is nothing more but a simple wrapper around the usual `.requires` predicate:
+
+```java
+Commands.literal("mycommand")
+    .requires(Commands.restricted(source -> source.getSender().hasPermission("my.custom.permission")
+                                            && source.getExecutor() instanceof Player player
+                                            && player.getGameMode() == GameMode.ADVENTURE))
+    .executes(ctx -> {
+        // Command logic
+    });
+```