chore: improve nesting error message

CHANGELOG.md

@@ -108,6 +108,9 @@ These changes are available on the `master` branch, but have not yet been releas
   ([#2099](https://github.com/Pycord-Development/pycord/pull/2099))
 - Changed the support from `orjson` to `msgspec` in the codebase.
   ([#2170](https://github.com/Pycord-Development/pycord/pull/2170))
+- Changed the error message that appears after an attempt at creating a subcommand group
+  under a subcommand group.
+  ([#2275](https://github.com/Pycord-Development/pycord/pull/2275))
 
 ### Removed
 

discord/commands/core.py

@@ -1303,8 +1303,9 @@ def create_subgroup(
         """
 
         if self.parent is not None:
-            # TODO: Improve this error message
-            raise Exception("a subgroup cannot have a subgroup")
+            raise Exception(
+                "A slash command group can only have one level of subcommand groups"
+            )
 
         sub_command_group = SlashCommandGroup(
             name, description, guild_ids, parent=self, **kwargs