Update CHANGELOG.md

Signed-off-by: Margaret Duff <43645617+MargaretDuff@users.noreply.github.com>

CHANGELOG.md

@@ -15,6 +15,7 @@
     - Add checks on out argument passed to processors to ensure corrrect dtype and size (#1805)
     - Internal refactor: Replaced string-based label checks with enum-based checks for improved type safety and consistency (#1692)
     - Internal refactor: Separate framework into multiple files (#1692)
+    - Allow the SIRT algorithm to take `initial=None` (#1906)
   - Testing:
     - New unit tests for operators and functions to check for in place errors and the behaviour of `out` (#1805)
     - Updates in SPDHG vs PDHG unit test to reduce test time and adjustments to parameters (#1898)