Update README

Signed-off-by: Matt DeVillier <matt.devillier@puri.sm>

README.md

-# utility
+# coreboot Utility and Updater Script
 
-coreboot utility and updater script. will consolidate functions from existing binary updater and build from source scripts
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+This coreboot utility and updater script consolidates functions from previous binary updater and build-from-source scripts.
+
+It provides the following functions:
+
+* Downloads a precompiled firmware update for a given device, with the choice between the standard (factory-shipped) legacy BIOS (SeaBIOS) firmware and our new Pureboot (coreboot + Heads) firmware
+
+* Downloads and compiles a standard coreboot/SeaBIOS firmware image for a given device
+
+* The option to flash a downloaded/compiled update, if running the standard/SeaBIOS firmware (users running Pureboot should copy the firmware file to USB and update via the Heads menu option)
+
+* The option to adjust the default boot order, if running the standard/SeaBIOS firmware.
+
+* The option to update/set the device serial number (not available for older 13v1/15v2 devices)
+
+
+## usage
+
+from a terminal, run:
+
+    wget https://source.puri.sm/coreboot/utility/raw/master/coreboot_util.sh
+    sudo bash coreboot_util.sh
+
+### 1) Update firmware using precompiled image
+
+This function will: 
+
+ * Prompt for device selection, attempting to detect and set the correct default option
+ * Prompt for firmware type selection (standard or Pureboot), for devices which have both options
+ * Prompt to confirm/enter the device serial number, defauting to current device serial
+ * Prompt to set the default bootorder, if standard firmware selected. The script will attempt to 
+ detect which drive types are present/installed on the current system, as well as offer an option
+ for externally-connected USB/SD devices.
+ * Download the appropriate firmware image based on user selection
+ * Inject the device serial and bootorder into the image (as needed)
+ * Provide the option to flash the firmware update, if currently running the standard firmware.
+ If running the PureBoot firmware, the user will be informed to copy the firmware update file to
+ USB and update via the Heads menu option
+
+ ###  2) Build firmware update from source
+
+ This function will:
+
+ * Prompt for device selection, attempting to detect and set the correct default option
+ * Prompt to confirm/enter the device serial number, defauting to current device serial
+ * Prompt to set the default bootorder
+ * Verify/download the required binary blobs, extracting from a precompiled coreboot image if needed
+ * Download the latest coreboot source from Purism's repo
+ * Verify/build the coreboot toolchain
+ * Build coreboot, SeaBIOS, and other secondary payloads from source
+ * Verify BIOS region of compiled firmware agianst known good hash
+ * Inject the device serial and bootorder into the image
+ * Provide the option to flash the firmware update, if currently running the standard firmware.
+ If running the PureBoot firmware, the user will be informed to copy the firmware update file to
+ USB and update via the Heads menu option
+
+ ### 3) Modify default boot order
+
+ This function will:
+
+ * Verify the current device firmware is the standard/SeabIOS firmware
+ * Prompt to set the default bootorder
+ * Download and/or build any required tools (cbfstool, flashrom)
+ * Read the current firmware from flash
+ * Remove old bootorder / inject new bootorder
+ * Provide the option to update the firmware with the new bootorder
+
+ ### 4) Set device serial number
+
+ This function will:
+
+ * Verify the current device firmware is the standard/SeabIOS firmware
+ * Prompt to confirm/enter the device serial number, defauting to current device serial
+ * Download and/or build any required tools (cbfstool, flashrom)
+ * Read the current firmware from flash
+ * Remove old serial number / inject new serial number
+ * Provide the option to update the firmware with the new serial number
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