[commands] Document exceptions being ignored in teardown and cog_unload

Co-authored-by: Josh <josh.ja.butt@gmail.com>

discord/ext/commands/cog.py

@@ -550,6 +550,8 @@ class Cog(metaclass=CogMeta):
 
         Subclasses must replace this if they want special unloading behaviour.
 
+        Exceptions raised in this method are ignored during extension unloading.
+
         .. versionchanged:: 2.0
 
             This method can now be a :term:`coroutine`.

docs/ext/commands/extensions.rst

@@ -54,6 +54,8 @@ Cleaning Up
 
 Although rare, sometimes an extension needs to clean-up or know when it's being unloaded. For cases like these, there is another entry point named ``teardown`` which is similar to ``setup`` except called when the extension is unloaded.
 
+Exceptions raised in the ``teardown`` function are ignored, and the extension is still unloaded.
+
 .. code-block:: python3
     :caption: basic_ext.py