Preps for 1.8.0-rc2

Update version fields for 1.8.0-rc2 release.

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/docs/release-notes.md b/docs/release-notes.md
index 60171f0..0b3e01c 100644
--- a/docs/release-notes.md
+++ b/docs/release-notes.md
@@ -26,6 +26,10 @@
 - Allow to boot primary image if secondary one is unreachable.
 - Add AES256 image encryption support.
 - Add Multiimage boot for direct-xip and ram-load mode.
+- Cargo files moved to top level, now `cargo test` can be run from the
+  top level directory.
+- Fault injection tests use updated TF-M.
+- Thingy:53 now supports multi-image DFU.
 
 ### Security fixes