Be more specific in add_command error message (#453)

* Be more specific in add_command error message

* Update changelog - v2.9.3

---------

Co-authored-by: Tom <[email protected]>

Author: aricodes-oss

docs/changelog.rst

@@ -1,10 +1,16 @@
 :orphan:
 
+
 2.10.0
 =======
 - TwitchIO
     - Bug fixes
         - fix: :func:`~twitchio.PartialUser.fetch_markers` was passing list of one element from payload, now just passes element
+
+- ext.commands
+    - Changes
+        - Added which alias failed to load in the error raised by :func:`~twitchio.ext.commands.Context.add_command`
+
 - ext.eventsub
     - Additions
         - Added :method:`Twitchio.ext.eventsub.EventSubClient.subscribe_channel_unban_request_create <EventSubClient.subscribe_channel_unban_request_create>` / 
@@ -78,7 +84,7 @@
         - New models for the new methods have been added:
             - :class:`~twitchio.ChannelFollowerEvent`
             - :class:`~twitchio.ChannelFollowingEvent`
-        - New optional ``is_featured`` query parameter for :func:`~twitchio.PartialUser.fetch_clips` 
+        - New optional ``is_featured`` query parameter for :func:`~twitchio.PartialUser.fetch_clips`
         - New attribute :attr:`~twitchio.Clip.is_featured` for :class:`~twitchio.Clip`
 
     - Bug fixes
@@ -116,14 +122,14 @@
         - Added :func:`~twitchio.Client.fetch_content_classification_labels` along with :class:`~twitchio.ContentClassificationLabel`
         - Added :attr:`~twitchio.ChannelInfo.content_classification_labels` and :attr:`~twitchio.ChannelInfo.is_branded_content` to :class:`~twitchio.ChannelInfo`
         - Added new parameters to :func:`~twitchio.PartialUser.modify_stream` for ``is_branded_content`` and ``content_classification_labels``
-            
+
     - Bug fixes
         - Fix :func:`~twitchio.Client.search_categories` due to :attr:`~twitchio.Game.igdb_id` being added to :class:`~twitchio.Game`
         - Made Chatter :attr:`~twitchio.Chatter.id` property public
         - :func:`~twitchio.Client.event_token_expired` will now be called correctly when response is ``401 Invalid OAuth token``
         - Fix reconnect loop when Twitch sends a RECONNECT via IRC websocket
         - Fix :func:`~twitchio.CustomReward.edit` so it now can enable the reward
-    
+
     - Other Changes
         - Updated the HTTPException to provide useful information when an error is raised.
 

twitchio/ext/commands/bot.py

@@ -209,7 +209,7 @@ def add_command(self, command: Command):
             if alias in self.commands:
                 del self.commands[command.name]
                 raise TwitchCommandError(
-                    f"Failed to load command <{command.name}>, a command with that name/alias already exists."
+                    f"Failed to load alias <{alias}> for command <{command.name}>, a command with that name/alias already exists.",
                 )
             self._command_aliases[alias] = command.name