Documentation/releases: Finalize 4.11, start 4.12

Fill in some stats using our repo analysis scripts in
util/release/, thank the contributors, add some prose
about notable achievements since 4.10.

Also start a new doc for 4.12.

Change-Id: I10a39081762d6e01f4040f717d36662975e4c8e9
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36948
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

Documentation/releases/coreboot-4.12-relnotes.md

@@ -0,0 +1,16 @@
+Upcoming release - coreboot 4.12
+================================
+
+The 4.12 release is planned for April 2020
+
+Update this document with changes that should be in the release
+notes.
+* Please use Markdown.
+* See the past few release notes for the general format.
+* The chip and board additions and removals will be updated right
+  before the release, so those do not need to be added.
+
+Significant changes
+-------------------
+
+### Add significant changes here