Chnaged Plugin Help Link for #3322

Plugin Help link got moved again into a new page of the docs.

Author: martinbndr

cogs/plugins.py

@@ -114,7 +114,7 @@ class Plugins(commands.Cog):
     These addons could have a range of features from moderation to simply
     making your life as a moderator easier!
     Learn how to create a plugin yourself here:
-    https://docs.modmail.dev/old-docs/plugins
+    https://docs.modmail.dev/usage-guide/plugins
     """
 
     def __init__(self, bot):