Update incorrect note in MOM_override

See https://github.com/COSIMA/access-om3/issues/251

Co-authored-by: minghangli-uni <[email protected]>

Author: anton-seaice

MOM_override

@@ -1,5 +1,2 @@
-! WARNING: DO NOT EDIT this file! Any user change made in this file will be
-!          overriden. This file is automatically generated. MOM6 parameter
-!          changes may be made via SourceMods or user_nl_mom.
-!-------------------------------------------------------------------------
-
+! NOTE: User made changes to this file override the settings in MOM_input
+!       This provides a clear record of how your configuration differs from the standard