Add info to "What's New" document

Author: barneygale

Doc/whatsnew/3.10.rst

@@ -812,6 +812,11 @@ Added negative indexing support to :attr:`PurePath.parents
 <pathlib.PurePath.parents>`.
 (Contributed by Yaroslav Pankovych in :issue:`21041`)
 
+Added :meth:`Path.hardlink_to <pathlib.Path.hardlink_to>` method that
+supersedes :meth:`~pathlib.Path.link_to`. The new method has the same argument
+order as :meth:`~pathlib.Path.symlink_to`.
+(Contributed by Barney Gale in :issue:`39950`.)
+
 platform
 --------
 
@@ -1150,6 +1155,10 @@ Deprecated
 
  (Contributed by Jelle Zijlstra in :issue:`21574`.)
 
+* :meth:`pathlib.Path.link_to` is deprecated and slated for removal in
+ Python 3.12. Use :meth:`pathlib.Path.hardlink_to` instead.
+ (Contributed by Barney Gale in :issue:`39950`.)
+
 
 Removed
 =======