Tweak global_scheduler changes file

changes/global_scheduler

@@ -1,4 +1,12 @@
- o Major changes:
+ o Major features (relay, infrastructure):
    - Implement a new inter-cmux comparison API, a global high/low watermark
      mechanism and a global scheduler loop for transmission prioritization
-     across all channels as well as among circuits on one channel.
+     across all channels as well as among circuits on one channel. This
+     schedule is currently tuned to (tolerantly) avoid making changes
+     in the current network performance, but it should form the basis
+     major circuit performance increases.  Code by Andrea; implements
+     ticket 9262.
+
+ o Testing:
+   - New tests for many parts of channel, relay, and circuit mux
+     functionality.  Code by Andrea; part of 9262.