DOC: clarify doc re: unsupported keys in savez.

The previous wording ("When saving dictionaries") could be interpreted
as refering to calls like `savez("foo.npz", {"a": 1, "b": 2})`
(literally "saving a dict to foo.npz"); reword to avoid this possibility
of confusion.

Author: anntzer

numpy/lib/npyio.py

@@ -581,9 +581,9 @@ def savez(file, *args, **kwds):
     its list of arrays (with the ``.files`` attribute), and for the arrays
     themselves.
 
-    When saving dictionaries, the dictionary keys become filenames
-    inside the ZIP archive. Therefore, keys should be valid filenames.
-    E.g., avoid keys that begin with ``/`` or contain ``.``.
+    Keys passed in `kwds` are used as filenames inside the ZIP archive.
+    Therefore, keys should be valid filenames; e.g., avoid keys that begin with
+    ``/`` or contain ``.``.
 
     When naming variables with keyword arguments, it is not possible to name a
     variable ``file``, as this would cause the ``file`` argument to be defined