Help: Add 3.13.5 release notes

Add a note about the fix in commit 3d3713121b (target_link_libraries:
Fix static library private deps in other dirs, 2019-04-30).
diff --git a/Help/release/3.13.rst b/Help/release/3.13.rst
index 1c58550..a8dd0ba 100644
--- a/Help/release/3.13.rst
+++ b/Help/release/3.13.rst
@@ -278,3 +278,12 @@
   relying on the old behavior can be trivially fixed by specifying
   the path to the source tree (even if just ``.``) explicitly and
   continue to work with all versions of CMake.
+
+3.13.5
+------
+
+* In CMake 3.13.0 through 3.13.4, calling :command:`target_link_libraries`
+  to add ``PRIVATE`` dependencies to a static library created in another
+  directory (under policy :policy:`CMP0079` ``NEW`` behavior) would
+  incorrectly propagate usage requirements of those dependencies to
+  dependents that link the static library.  This has been fixed.