Documentation: Mention newer Intel μ-code updates in 4.13 release notes

Start a new section *Notes* for these kind of information.

Change-Id: I86be22cebb96e6f07676a9bc52794a4c12dad3e4
Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/47762
Reviewed-by: Michael Niewöhner <foss@mniewoehner.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

Documentation/releases/coreboot-4.13-relnotes.md

@@ -234,3 +234,27 @@ to ensure that the platforms listed above are fixed before the next release. If
 is interest in maintaining support for these platforms beyond the next release,
 please ensure that the platforms are fixed to conform to the expectations of resource
 allocation.
+
+Notes
+-----
+
+### Intel microcode updates
+
+Intel microcode updates tagged *microcode-20200616* are still included in our
+builds. Note, [Intel released new microcode updates]
+(https://github.com/intel/Intel-Linux-Processor-Microcode-Data-Files/blob/main/releasenote.md)
+tagged
+
+1.  *microcode-20201110*
+2.  *microcode-20201112*
+3.  *microcode-20201118*
+
+with security updates for [INTEL-SA-00381]
+(https://www.intel.com/content/www/us/en/security-center/advisory/intel-sa-00381.html)
+and [INTEL-SA-00389]
+(https://www.intel.com/content/www/us/en/security-center/advisory/intel-sa-00389.html).
+
+Due to too short time for rigorous testing and bad experience with botched
+microcode updates in the past, these new updates are not included. Users wanting
+to use those, can apply them in the operating system, or update the submodule
+pointer themselves.