[commands] Export max_concurrency and MaxConcurrencyReached in docs

docs/ext/commands/api.rst

@@ -170,6 +170,8 @@ Checks
 
 .. autofunction:: discord.ext.commands.cooldown
 
+.. autofunction:: discord.ext.commands.max_concurrency
+
 .. autofunction:: discord.ext.commands.guild_only
 
 .. autofunction:: discord.ext.commands.dm_only
@@ -325,6 +327,9 @@ Exceptions
 .. autoexception:: discord.ext.commands.CommandOnCooldown
     :members:
 
+.. autoexception:: discord.ext.commands.MaxConcurrencyReached
+    :members:
+
 .. autoexception:: discord.ext.commands.NotOwner
     :members:
 
@@ -401,6 +406,7 @@ Exception Hierarchy
             - :exc:`~.commands.DisabledCommand`
             - :exc:`~.commands.CommandInvokeError`
             - :exc:`~.commands.CommandOnCooldown`
+            - :exc:`~.commands.MaxConcurrencyReached`
         - :exc:`~.commands.ExtensionError`
             - :exc:`~.commands.ExtensionAlreadyLoaded`
             - :exc:`~.commands.ExtensionNotLoaded`