Update CHANGELOG for libaom v3.4.0 (continued)

Add updates from Ittiam and Marco.

Bug: aomedia:3281
Change-Id: I5b2ec54744f20a3fc967000466a29498254d9dba

CHANGELOG

-2022-06-16 v3.4.0
+2022-06-17 v3.4.0
   This release includes compression efficiency and perceptual quality
   improvements, speedup and memory optimizations, and some new features.
   There are no ABI or API breaking changes in this release.
@@ -35,7 +35,7 @@
   - Compression Efficiency Improvements
     * Correctly calculate SSE for high bitdepth in skip mode, 0.2% to
       0.6% coding gain.
-    * RTC at speed 9/10: BD-rate gain of ~4/5% and speedup of ~10/5%
+    * RTC at speed 9/10: BD-rate gain of ~4/5%
     * RTC screen content coding: many improvements for real-time screen
       at speed 10 (quality, speedup, and rate control), up to high
       resolutions (1080p).
@@ -51,10 +51,18 @@
 
   - Speedup and Memory Optimizations
     * ~10% speedup in good quality mode encoding.
+    * ~7% heap memory reduction in good quality encoding mode for speed
+      5 and 6.
     * Ongoing improvements to intra-frame encoding performance on Arm
     * Faster encoding speed for "--deltaq-mode=3" mode.
-    * Improved encoding speed for real time mode speeds 5 and 6 with
-      default settings
+    * ~10% speedup for speed 5/6, ~15% speedup for speed 7/8, and
+      ~10% speedup for speed 9/10 in real time encoding mode
+    * ~20% heap memory reduction in still-picture encoding mode for
+      360p-720p resolutions with multiple threads
+    * ~13% speedup for speed 6 and ~12% speedup for speed 9 in
+      still-picture encoding mode.
+    * Optimizations to improve multi-thread efficiency for still-picture
+      encoding mode.
 
   - Bug Fixes
     * b/204460717: README.md: replace master with main