migration-guides: add release notes for 4.0.13

(From yocto-docs rev: ceb1812e63b9fac062f886c2a1dde23137c0e1ed)

Signed-off-by: Lee Chee Yang <chee.yang.lee@intel.com>
Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/migration-guides/release-4.0.rst

@@ -19,3 +19,4 @@ Release 4.0 (kirkstone)
    release-notes-4.0.10
    release-notes-4.0.11
    release-notes-4.0.12
+   release-notes-4.0.13