Update changelog with 5.2.2 entry

Author: andersfugmann

Changelog

@@ -9,6 +9,10 @@ Changes marked with '*' indicates a changes that breaks backward compatibility
 [ ] Add namespaces to attributes
 [ ] Unify xmlm and xml_light driver to share codebase
 
+5.2.2
+[x] Fix compatability with Ocaml 5
+[x] Avoid linking against ppxlib
+
 5.2.1
 [x] Set minimum ocaml version to 4.08
 [x] Remove warnings on using kprintf and switch to reference Stdlib and not Caml