Add changelog entry for reworked UI backends

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

Changelog.draft.rst

@@ -23,6 +23,14 @@ Changes
 
 * Output how long an account sync took (min:sec).
 
+* Reworked logging which was reported to e.g. not flush output to files
+  often enough. User-visible changes:
+  a) console output goes to stderr (for now).
+  b) file output has timestamps and looks identical in the basic and
+  ttyui UIs.
+  c) File output should be flushed after logging by default (do
+  report if not).
+
 Bug Fixes
 ---------