add warning for remote import

remote import handle aliasing does not work, as told in the docs. This is kind of unexpected, as it worked locally, without any warning, resulting in asymmetric module handles.

docs/source/parallel/parallel_multiengine.rst

@@ -509,7 +509,10 Any imports made inside the block will also be performed on the view's engines.
 sync_imports also takes a `local` boolean flag that defaults to True, which specifies
 whether the local imports should also be performed.  However, support for `local=False`
 has not been implemented, so only packages that can be imported locally will work
-this way.
+this way. Note, that the usual renaming of the import handle in the same line like in
+`import matplotlib.pyplot as plt' does not work on the remote engine, the `as plt` is 
+ignored remotely, while it executes locally. One could rename the remote handle with
+`%px plt = pyplot` though after the import.
 
 You can also specify imports via the ``@require`` decorator.  This is a decorator
 designed for use in Dependencies, but can be used to handle remote imports as well.