adds C++ features to change log (#22906)

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>
Co-authored-by: Juan Carlos <juancarlospaco@gmail.com>

changelog.md

@@ -32,6 +32,9 @@ slots when enlarging a sequence.
 ## Language changes
 
 - `noInit` can be used in types and fields to disable member initializers in the C++ backend. 
+- C++ custom constructors initializers see https://nim-lang.org/docs/manual_experimental.htm#constructor-initializer
+- `member` can be used to attach a procedure to a C++ type.
+- C++ `constructor` now reuses `result` instead creating `this`.
 
 ## Compiler changes