Added release notes and improved documentation for append_images [ci skip]

docs/handbook/image-file-formats.rst

@@ -104,8 +104,10 @@ Saving sequences
 When calling :py:meth:`~PIL.Image.Image.save`, if a multiframe image is used,
 by default only the first frame will be saved. To save all frames, the
 ``save_all`` parameter must be present and set to ``True``. To append
-additional frames when saving, the ``append_images`` parameter can be set to a
-list of images containing the extra frames.
+additional frames when saving, the ``append_images`` parameter works with
+``save_all`` to append a list of images containing the extra frames::
+
+    im.save(out, save_all=True, append_images=[im1, im2, ...])
 
 If present, the ``loop`` parameter can be used to set the number of times
 the GIF should loop, and the ``duration`` parameter can set the number of

docs/releasenotes/3.4.0.rst

@@ -13,3 +13,16 @@ two times shorter window than ``BILINEAR``. It can be used for image reduction
 ``HAMMING`` filter has the same performance as ``BILINEAR`` filter while
 providing the image downscaling quality comparable to ``BICUBIC``.
 Both new filters don't show good quality for the image upscaling.
+
+
+Append images to GIF
+====================
+
+Additional frames can now be appended when saving a GIF file, through the
+``append_images`` argument. The new frames are passed in as a list of images,
+which may be have multiple frames themselves.
+
+Note that the ``append_images`` argument is only used if ``save_all`` is also
+in effect, e.g.::
+
+    im.save(out, save_all=True, append_images=[im1, im2, ...])