Add a warning to the docs about $args in ExecAlias (#5033)

docs/tutorial.rst

@@ -1264,6 +1264,16 @@ or by the index in ``$arg<n>`` environment variables.
     >>> aliases['piu'] = 'pip install -U @($args)'
     >>> aliases['cdls'] = 'cd $arg0 && ls'
 
+.. warning:: That means, if you need ``@()`` in your alias, you can't rely on
+             automatic argument handling anymore. Any alias involving it needs
+             to add ``$args`` at the end manually if you don't want your alias
+             to ignore supplied arguments.
+
+.. code-block:: xonshcon
+
+    >>> aliases['careful'] = 'echo @("all args will be ignored")'
+    >>> aliases['better'] = 'echo @("the arguments are: ") @($args)'
+
 .. note::
 
    To add multiple aliases there is merge operator: ``aliases |= {'e': 'echo', 'g': 'git'}``.