[commands] Add note for command tree in Bot's docstring

discord/ext/commands/bot.py

@@ -1289,6 +1289,10 @@ class Bot(BotBase, discord.Client):
     This class also subclasses :class:`.GroupMixin` to provide the functionality
     to manage commands.
 
+    Unlike :class:`discord.Client`, This class does not require manually setting
+    a :class:`~discord.app_commands.CommandTree` and is automatically set upon
+    instantiating the class.
+
     Attributes
     -----------
     command_prefix