updated release notes (UX improvements, bugfixes, etc.)

RELEASE_NOTES.md

@@ -44,9 +44,48 @@ changes (where available).
 
 - ???
 
+## UI/UX Improvements
+
+- Added camera-specific styles for more than 500 camera models to more
+  closely approximate the out-of-camera JPEG rendition.  These styles
+  only affect contrast, brightness, and saturation and do not attempt
+  to match sharpening, denoising, or hue shifts.  Also added a LUA
+  script to auto-apply the appropriate style on import and manually
+  apply styles to a collection of previously-imported images.
+
+- The user interface now gives feedback while processing bulk image
+  operations such as ratings, tagging, and edit history management,
+  rather than silently freezing until the operation completes.  While
+  the operation is in progress, darktable will now show either a busy
+  cursor (such as a stopwatch or spinner) or a progress bar with
+  option to cancel the remainder of the operation.
+
+- Added a high-contrast theme with bright white text on a dark gray
+  background.
+
+- Enhanced tooltips for utiltity module headers to provide more
+  information about the module.
+
+- Added more hints on an empty lighttable.
+
+- Added two new error placeholder images to distinguish between
+  missing, unsupported, and corrupted images.  When attempting to edit
+  such an image, an appropriate, more specific error message is
+  displayed.
+
+- When selecting a style in the export module, hovering on the style
+  name in the popup menu displays a thumbnail previewing the effect of
+  appending the style to the active image's edit (first selected image
+  in lighttable, center-view image in darkroom).
+
 ## Performance Improvements
 
-- ???
+- Added OpenCL implementation of color equalizer.
+
+- Improved the speed of bulk image operations by improving the speed
+  of sidecar writes, and by moving sidecar updates for many operations
+  into a background task, allowing the user to proceed before the
+  writes complete.
 
 ## Other Changes
 
@@ -57,13 +96,34 @@ changes (where available).
 - The ISO 12646 color assessment condition is kept until unset by user
   action.
 
-- Enhanced tooltips for utiltity module headers to provide more
-  information about the module.
+- Exposure bias can now be used to form collections and as a display filter.
+
+- Improved visualization of the color equalizer's effect.
+
+- Improved debugging support for verifying CPU vs. GPU results.
+
+- Add Calibrite alias for X-Rite ColorChecker in color calibration.
+
+- Numerous rounds of code cleanup.
 
 ## Bug Fixes
 
 - Fixed a performance regression for redrawing mipmaps.
 
+- Fixed handling of old (2020) edits using Filmic RGB.
+
+- Various OpenCL fixes to reduce differences between CPU and GPU processing: colorspace conversion, saturation gradient filter in color equalizer.
+
+- Fixed gallery export not working on Windows.
+
+- Fixed printer discovery in the print module, which could cause available printers to be missed.
+
+- Work around out-of-spec ExIF date field caused by buggy software.
+
+- Fixed reading embedded color profiles from PNG images.
+
+- Fixed certain boundary cases in the crop module.
+
 ## Lua
 
 ### API Version