Updated the documentation for the Raspberry Pi 4 bootloader. Closes #23.

README.md

@@ -17,18 +17,18 @@ generate the following artifacts:
 cross development toolchain for C and C++.
 * An emulated arm64 or armhf LXD container.
 
-:warning: **Raspberry Pi 4 boot loader**: On the Raspberry Pi 4 the
-[stock boot loader](https://github.com/raspberrypi/firmware)
-does load the device tree binary and modifies it. For this reason it is difficult to
-do a robust update of the kernel together with the device tree binary. For now, edi-pi
-does not touch the device tree binary that gets loaded by the stock boot loader during
-a robust update and the boot process will just take over the device tree that got loaded
-by the stock boot loader instead of taking the one that gets bundled with the kernel.
-This might be a setup that is not sustainable for industrial applications that require
-long term support. For such scenarios you might want to consider other platforms such as
-[edi-var](https://github.com/lueschem/edi-var/) and
-[edi-cl](https://github.com/lueschem/edi-cl/). If I find a solid solution for the described
-boot loader issue I will update the configuration accordingly.
+:warning: **New Raspberry Pi 4 boot loader integration**: Starting with Debian bullseye
+the Raspberry Pi 4 setup with regards to the boot loader integration has changed: Instead of
+U-Boot the setup now directly relies upon the Raspberry Pi boot loader. The new "tryboot feature"
+together with a custom Mender integration allowed us to solve the
+[device tree handling during A/B updates issue](https://github.com/lueschem/edi-pi/issues/23). To
+make use of this new setup a
+[recent (>=2021-04-19) bootloader EEPROM](https://github.com/raspberrypi/rpi-eeprom/blob/master/firmware/release-notes.md)
+is required. **Please upgrade your Raspberry Pi 4 EEPROM prior to using this new setup.**
+Unfortunately this **new boot loader integration is incompatible with the previous setup**.
+Additional work would be required to migrate an existing installation over the air from the previous
+setup to this new setup. At the moment an existing installation using the old boot loader setup will need to be re-flashed.
+As the new boot loader integration required quite some rework, some rough edges are still to be expected.
 
 ## Important Note
 
@@ -210,6 +210,7 @@ Then the pdf can be generated using the following commands:
 ``` bash
 cd artifacts/CONFIGNAME_documentation
 make PDFLATEX=xelatex latexpdf
+make PDFLATEX=xelatex latexpdf
 ```
 
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