README.md: Add notes about iopl and AC adapter requirement

In order for the EC to maintain the state of whether or not to set the
flash descriptor override across a power cycle, the AC adapter must be
connected, as the system leaves the voltage rail that the EC uses
powered under this condition. Without this, the utility may fail,
continually asking the user to power off and on.

On Linux, CONFIG_X86_IOPL_IOPERM must be set for the kernel, or else the
iopl call will error with "Function not implemented". Make a note of
this in case a user runs into this issue.

Signed-off-by: Nicholas Chin <nic.c3.14@gmail.com>

util/dell-flash-unlock/README.md

@@ -8,10 +8,26 @@ E6400, which mainly seem to be the Latitude and Precision lines starting from
 around 2008 (E6400 era).
 
 ## TL;DR
-On Linux, ensure you are booting with the `iomem=relaxed` kernel parameter.
-On OpenBSD, ensure you are booting with securelevel set to -1.
-Run `make` to compile the utility, and then run `sudo ./dell_flash_unlock` and
-follow the directions it outputs.
+
+### Linux specific
+- On Linux, ensure you are booting with the `iomem=relaxed` kernel parameter.
+- If you get a "Function not implemented" error, ensure that your kernel has
+  "CONFIG_X86_IOPL_IOPERM" set to "y". Here are several common locations for
+  the config and how to check them:
+  - `zcat /proc/config.gz | grep IOPL`
+  - `grep IOPL /boot/config`
+  - `grep IOPL /boot/config-$(uname -r)`
+  If it says it is not set, then you will need to install or compile a kernel
+  with that option set.
+
+### OpenBSD
+- On OpenBSD, ensure you are booting with securelevel set to -1.
+
+### General
+Make sure an AC adapter is plugged into your system
+
+Run `make` to compile the utility, and then run `./dell_flash_unlock` with
+root/superuser permissions and follow the directions it outputs.
 
 ## Confirmed supported devices
 - Latitude E6400, E6500