Update release notes

docs/releasenotes/5.4.0.rst

@@ -1,9 +1,29 @@
-5.4.0 (unreleased)
+5.4.0
 -----
 
 API Changes
 ===========
 
+APNG extension to PNG plugin
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Animated Portable Network Graphics (APNG) images are not fully supported but
+can be opened via the PNG plugin to get some basic info::
+
+    im = Image.open("image.apng")
+    print(im.mode)  # "RGBA"
+    print(im.size)  # (245, 245)
+    im.show()  # Shows a single frame
+
+Check for libjpeg-turbo
+^^^^^^^^^^^^^^^^^^^^^^^
+
+You can check if Pillow has been built against the libjpeg-turbo version of the
+libjpeg library::
+
+    from PIL import features
+    features.check_feature("libjpeg_turbo")  # True or False
+
 Negative indexes in pixel access
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
@@ -15,6 +35,26 @@ For example, to get or set the farthest pixel in the lower right of an image::
     px[-1, -1] = (0, 0, 0)
 
 
+New custom TIFF tags
+^^^^^^^^^^^^^^^^^^^^
+
+TIFF images can now be saved with custom integer, float and sting TIFF tags::
+
+    im = Image.new("RGB", (200, 100))
+    custom = {
+        37000: 4,
+        37001: 4.2,
+        37002: "custom tag value",
+        37003: u"custom tag value",
+        37004: b"custom tag value",
+    }
+    im.save("output.tif", tiffinfo=custom)
+
+    im2 = Image.open("output.tif")
+    print(im2.tag_v2[37000])  # 4
+    print(im2.tag_v2[37002])  # "custom tag value"
+    print(im2.tag_v2[37004])  # b"custom tag value"
+
 Other Changes
 =============