docs: release-notes: Add note on changes

Adds release notes based on these changes

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>

docs/release-notes.d/zephyr-compression.md

@@ -0,0 +1,7 @@
+- Added protected TLV size to image size check in bootutil
+- Added Kconfig for decompression support in Zephyr
+- Added compressed image flags and TLV to bootutil
+- Added support for removing images with conflicting flags in
+  bootutil
+- Added support for removing encrypted/compressed images when
+  MCUboot is compiled without support for them