Add items to the soft deprecations document

Author: srittau

Doc/deprecations/soft-deprecations.rst

@@ -19,3 +19,19 @@ There are no plans to remove :term:`soft deprecated` APIs.
 
   (Contributed by Gregory P. Smith in :gh:`86519` and
   Hugo van Kemenade in :gh:`148100`.)
+
+* The following typing-related classes are :term:`soft deprecated`:
+
+  * :class:`typing.Optional` in favor of the dedicated union syntax
+    (``X | None``)
+  * :class:`typing.NoReturn` in favor of :class:`typing.Never`
+  * :class:`typing.ForwardRef` in favor of :class:`annotationlib.ForwardRef`
+  * :class:`types.UnionType` in favor of :class:`typing.Union` (but see below)
+
+  Creating :class:`typing.Union` instances using the constructor is also
+  deprecated. Use the dedicated union syntax (``X | Y``) instead.
+
+  Explicitly inheriting from :class:`typing.Generic` is also deprecated.
+  Use the dedicated syntax for :ref:`generic functions <generic-functions>`,
+  :ref:`generic classes <generic-classes>`, and
+  :ref:`generic type aliases <generic-type-aliases>` instead.