README: Document firmware updates

Document firmware updates for Qualcomm Linux Debian images. The devices
are expected to support UEFI firmware capsule updates. On the OS side,
the standard mechanism for firmware updates known as LVFS or fwupd is
leverage to update firmware on devices.

Note here that currently firmware for devices supported by Qualcomm
Linux isn't yet available/pushed on LVFS (WIP). Hence, the fwupdtool is
used currently for testing purposes.

Signed-off-by: Sumit Garg <[email protected]>

Author: b49020

README.md

@@ -6,6 +6,29 @@ Initially, this repository provides [debos](https://github.com/go-debos/debos) r
 
 We are also working towards providing ready-to-use, pre-built images – stay tuned!
 
+## Firmware updates
+
+On standard Linux distros like Debian, firmware updates are generally delivered via Linux Vendor Firmware Service ([LVFS](https://fwupd.org/)). The OEM/ODM vendors usually upload latest firmware releases on LVFS (refer [here](https://lvfs.readthedocs.io/en/latest/upload.html)) as cabinet (.cab) firmware archive files containing at least one metadata (.metainfo.xml) file describing the firmware update. On the device, fwupd is installed which provides a system-activated daemon listening on D-Bus for installing any firmware updates. On a Desktop system, its usually GNOME Software which monitors LVFS for any firmware updates and pushes to fwupd if any. On a headless system like most emdebbed devices, the fwupdmgr command line tool can be used to monitor LVFS for firmware updates as follows:
+
+```bash
+# Download latest metadata from LVFS
+fwupdmgr refresh
+
+# Fetch device specific firmware updates from LVFS
+fwupdmgr get-updates
+
+# Install firmware updates
+fwupdmgr update
+```
+
+The firmware on Qualcomm devices is expected to support UEFI UpdateCapsule plugin for fwupd daemon. However, currently firmware for Qualcomm devices in not available in LVFS which is a work in progress as of now. In order to play with UEFI firmware capsule updates, one can use fwupdtool to locally update firmware like on RB1 as follows:
+
+```bash
+# Transfer U-Boot firmware cabinet archive build from scripts/build-u-boot-rb1.sh to RB1
+sudo fwupdtool install u-boot.cab
+# It will ask for a reboot for the UEFI firmware capsule update to happen
+```
+
 ## Branches
 
 main: Primary development branch. Contributors should develop submissions based on this branch, and submit pull requests to this branch.