README.md: Various updates

Various bits.

Closes: #1

README.md

@@ -25,27 +25,41 @@ OS update system agnostic tool to manage updates for things like:
 
 This project originated in [this Fedora CoreOS github issue](https://github.com/coreos/fedora-coreos-tracker/issues/510).
 
+The scope is otherwise limited; for example, bootupd will not
+manage anything related to the kernel such as kernel arguments;
+that's for tools like `grubby` and `ostree`.
+
 ## Status
 
 Currently a work in progress and is not ready to ship for production
 updates, but early feedback on the design is appreciated!
 
 ## Relationship to other projects
 
+### dbxtool
+
+[dbxtool](https://github.com/rhboot/dbxtool) manages updates
+to the Secure Boot database - `bootupd` will likely need to
+perform any updates to the `shimx64.efi` binary
+*before* `dbxtool.service` starts.  But otherwise they are independent.
+
 ### fwupd
 
 bootupd could be compared to [fwupd](https://github.com/fwupd/fwupd/) which is
 project that exists today to update hardware device firmware - things not managed
 by e.g. `apt/zypper/yum/rpm-ostree update` today.
 
-fwupd comes as a UEFI binary today, so bootupd would actually take care of updating fwupd itself.
-
-The end result is that a system administrator would have 3 projects to monitor
-(one for hardware devices and 2 for the bootloader and OS state) but each
-would be clearly focused on its domain and handle it well.  This stands
-in contrast with e.g. having an RPM `%post` script try to regenerate the BIOS MBR.
+fwupd comes as a UEFI binary today, so bootupd *could* take care of updating `fwupd`
+but today fwupd handles that itself.  So it's likely that bootupd would only take
+care of GRUB and shim.  See discussion in [this issue](https://github.com/coreos/bootupd/issues/1).
 
 ### systemd bootctl
 
 [systemd bootctl](https://man7.org/linux/man-pages/man1/bootctl.1.html) can update itself;
 this project would probably just proxy that if we detect systemd-boot is in use.
+
+## Other goals
+
+One idea is that bootupd could help support [redundant bootable disks](https://github.com/coreos/fedora-coreos-tracker/issues/581).
+For various reasons it doesn't really work to try to use RAID1 for an entire disk; the ESP must be handled
+specially.  `bootupd` could learn how to synchronize multiple EFI system partitions from a primary.