Add a simple /help command

src/main/java/emu/lunarcore/command/commands/HelpCommand.java

@@ -0,0 +1,26 @@
+package emu.lunarcore.command.commands;
+
+import emu.lunarcore.LunarCore;
+import emu.lunarcore.command.Command;
+import emu.lunarcore.command.CommandArgs;
+import emu.lunarcore.command.CommandHandler;
+import emu.lunarcore.game.player.Player;
+
+@Command(label = "help", permission = "player.help", desc = "/help. Displays a list of available commands.")
+public class HelpCommand implements CommandHandler {
+
+    @Override
+    public void execute(Player sender, CommandArgs args) {
+        StringBuilder help = new StringBuilder();
+        this.sendMessage(sender, "Displaying list of commands:");
+        
+        var labels = LunarCore.getCommandManager().getLabels().keySet().stream().sorted().toList();
+        for (var label : labels) {
+            Command command = LunarCore.getCommandManager().getLabels().get(label).getClass().getAnnotation(Command.class);
+            if (command == null) continue;
+            
+            this.sendMessage(sender, command.desc());
+        }
+    }
+
+}