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-encryption-single.md b/docs/release-notes.d/zephyr-encryption-single.md
new file mode 100644
index 0000000..78767db
--- /dev/null
+++ b/docs/release-notes.d/zephyr-encryption-single.md
@@ -0,0 +1,3 @@
+- Zephyr: Fix issue with single application slot mode, serial
+  recovery and encryption whereby an encrypted image is loaded
+  and being wrongly treated as encrypted after decryption.