Help: Add 3.13.4 release note for no source/build dir error/warning

Help/release/3.13.rst

@@ -252,3 +252,29 @@ Changes made since CMake 3.13.0 include the following.
   directories to the ``moc`` tool for :prop_tgt:`AUTOMOC`.  This has
   been reverted due to regressing existing builds and will need
   further investigation before being re-introduced in a later release.
+
+3.13.3
+------
+
+* The :generator:`Visual Studio 15 2017` generator has been fixed to work
+  when VS 2019 is installed.
+
+* CMake now checks that at least one of the source or binary directory
+  is specified when running CMake and issues an error if both are missing.
+  This has always been a documented requirement, but the implementation
+  previously accidentally accepted cases in which neither are specified
+  so long as some other argument is given, and silently used the current
+  working directory as the source and build tree.
+
+3.13.4
+------
+
+* The error added by 3.13.3 in cases that neither a source or binary
+  directory is specified has been downgraded to a warning.  While this
+  was never intended, documented, nor supported behavior, some projects
+  relied on it.  The error has been downgraded to a warning for the
+  remainder of the 3.13.x release series to allow a transition period,
+  but it may become a fatal error again in a later release.  Scripts
+  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.