note backups in release notes

RELEASE-v0.9.md

@@ -271,6 +271,13 @@ perform the Xous firmware upgrade. This requires running manual update commands,
 - Added a sanity check to the backup.py to make sure that the backup preparation was run: you must prepare backups every time before doing a backup. The exported key headers are erased after the backup is run, because you don't want the exported keys just laying around where anyone can read it out by plugging in a USB cable. Unfortunately, a user lost data because this check was missing :(
 - Added crates.io package verification to `xtask`. Note: Cargo.toml files are munged by `cargo publish`, so it's difficult to prove equivalence of your source file and what you're sent from crates.io. Instead, there's now a check in CI to confirm that Cargo.lock did not change, which should change with a tampered Cargo.toml.
 - Fixed cache coherence issue in FLASH. Writes to flash memory need to also invalidate D$ because they are out of band to the regular memory hierarchy.
+- Add checksums to backups
+  - every 1MiB block of the PDDB is checksummed with a SHA-512 hash, of which the first 128 bits are stored in a table
+  - checksums are included in the backup header
+  - `backalyzer.py`, `backup.py`, and `restore.py` now parse the header and if checksums are there, it will flag if there is a checksum error
+  - backups now take about an extra minute to run, due to the inclusion of the extra checksums
+  - backups are no longer abortable, because in order to do the checksums, we have to unmount the PDDB and put the system into a semi-shutdown state. A confirmation screen now gates backups to avoid users accidentally triggering backups with a fat-fingered menu selection.
+
 
 ## Roadmap to 1.0