[commands] Document BucketType separately

docs/ext/commands/api.rst

@@ -111,6 +111,38 @@ Help Commands
 .. autoclass:: discord.ext.commands.Paginator
     :members:
 
+Enums
+------
+
+.. class:: discord.ext.commands.BucketType
+
+    Specifies a type of bucket for, e.g. a cooldown.
+
+    .. attribute:: default
+
+        The default bucket operates on a global basis.
+    .. attribute:: user
+
+        The user bucket operates on a per-user basis.
+    .. attribute:: guild
+
+        The guild bucket operates on a per-guild basis.
+    .. attribute:: channel
+
+        The channel bucket operates on a per-channel basis.
+    .. attribute:: member
+
+        The member bucket operates on a per-member basis.
+    .. attribute:: category
+
+        The category bucket operates on a per-category basis.
+    .. attribute:: role
+
+        The role bucket operates on a per-role basis.
+
+        .. versionadded:: 1.3.0
+
+
 .. _ext_commands_api_checks:
 
 Checks