Add dualboot guide (#54)

Co-authored-by: Nathaniel van Diepen <Eeems@users.noreply.github.com>

src/spelling_wordlist.txt

@@ -6,6 +6,8 @@ bugfixes
 Carta
 changescrn
 chroot
+codex
+codexctl
 config
 cryptographic
 DBus
@@ -17,6 +19,8 @@ distro
 distros
 dotnet
 Dropbear
+dualboot
+dualbooting
 eInk
 entware
 epubs
@@ -50,6 +54,7 @@ reimplements
 reMarkable
 remux
 rM
+rmfakecloud
 rmKit
 rMlib
 rsa
@@ -70,6 +75,7 @@ Unregister
 usb
 userspace
 utils
+wget
 wifi
 wpa
 xochitl

src/tech/dualboot.rst

@@ -0,0 +1,77 @@
+==========================
+Dualbooting the reMarkable
+==========================
+
+.. contents:: Contents
+   :local:
+   :backlinks: none
+
+:raw-html:`<div class="warning">⚠️ Before starting ⚠️<br/>`
+
+This guide requires :doc:`../guide/access/ssh`
+
+:raw-html:`</div>`
+
+Choosing the versions
+=====================
+
+Before starting, you should know what versions to dualboot, depending on hat you want to do. For toltec, it is recommended to follow :doc:`this guide <../guide/software/toltec>`, while for rM hacks, you should read `the table on their github repo <https://github.com/mb1986/rm-hacks>`_.
+
+Downgrading/Upgrading the OS
+============================
+
+For more information on how to install a specific OS version see :ref:`upgrade`.
+
+Installing the switch service
+=============================
+
+While this is already a dualboot, it is very impractical, as you need to use `switch.sh <https://github.com/ddvk/remarkable-update/tree/main?tab=readme-ov-file#to-switch-the-partition-ie-boot-the-previous-version>`_ every time. 
+
+`FouzR/rM_dualboot <https://github.com/FouzR/rM_dualboot>`_ handles setting up both partitions to automatically run ``switch.sh`` every time the device is rebooted.
+
+Installing rM-hacks
+===================
+
+To install rm-hacks, follow the `rm-hacks installation instructions` <https://github.com/mb1986/rm-hacks?tab=readme-ov-file#installation>`_. After this, you will need to make changes to ensure that it doesn't get removed when you reboot into the other partition. There are two ways to handle this. The recommended way is to change the ``QML_DISK_CACHE_PATH`` environment variable. The other option would be to bind mount 
+``/home/root/.cache/remarkable/xochitl/qmlcache/`` to a different location.
+
+Editing the ``QML_DISK_CACHE_PATH`` variable
+--------------------------------------------
+
+The ``QML_DISK_CACHE_PATH`` variable specifies the `QML <https://doc.qt.io/qt-5/qmlapplications.html>`_ cache path of a `Qt application <https://doc.qt.io/qt-5/index.html>`_. This caches the code that is used to generate the xochitl GUI and handle many of it's interactions. When a version of xochitl is launched that does not match the current cache, it is removed and a new cache generated. This will wipe rm-hacks when dual booting, so we will need to setup a new location for the cache.
+
+Setting it on toltec
+____________________
+
+If you are running toltec on the second partition you can create an environment override for xochitl that will set the ``QML_DISK_CACHE_PATH``.
+
+.. code-block:: shell
+
+  mkdir -p /home/root/.cache/qmlcache
+  cat > /opt/etc/xochitl.env.d/99-override-qmldir.env << EOF
+  export QML_DISK_CACHE_PATH="/home/root/.cache/qmlcache"
+  EOF
+
+Setting it without toltec
+_________________________
+
+If you are not running toltec, you can override the xochitl ``QML_CACHE_PATH`` using systemd override files. 
+
+.. code-block:: shell
+
+  # Create overrides folder
+  mkdir /etc/systemd/system/xochitl.service.d
+  # Create override
+  cat > /etc/systemd/system/xochitl.service.d/override-qmlcache.conf << EOF
+  [Service]
+  Environment=QML_DISK_CACHE_PATH="/home/root/.qml/"
+  EOF
+  # Reload units
+  systemctl daemon-reload
+  # Restart xochitl
+
+
+Using rmfakecloud
+=================
+
+The cloud must be `configured <https://ddvk.github.io/rmfakecloud/remarkable/setup>` on both partitions, as it will otherwise get disconnected at every reboot due to an invalid login token.