Help: Add release note about XCODE_FILE_ATTRIBUTES source file property

Help/release/dev/xcode-file-attributes.rst

@@ -0,0 +1,6 @@
+xcode-file-attributes
+---------------------
+
+* A :prop_sf:`XCODE_FILE_ATTRIBUTES` source file property was
+  added to tell the :generator:`Xcode` generator to generate
+  custom content in the Xcode project attributes for the file.