docs: release: Add release notes

Adds release notes for various recent changes

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>
diff --git a/docs/release-notes.d/zephyr-estimated-sysbuild.mc b/docs/release-notes.d/zephyr-estimated-sysbuild.mc
new file mode 100644
index 0000000..8b42c26
--- /dev/null
+++ b/docs/release-notes.d/zephyr-estimated-sysbuild.mc
@@ -0,0 +1 @@
+- Zephyr: Add estimated image footer size to cache in sysbuild.