installation/guides/arm-devices: add x13s page

Author: classabbyamp

src/installation/guides/arm-devices/thinkpad-x13s.md

@@ -0,0 +1,45 @@
+# Lenovo ThinkPad X13s
+
+The Lenovo ThinkPad X13s Snapdragon-based laptop is supported on kernel 6.8 and
+higher, with some caveats. See [jhovold's
+wiki](https://github.com/jhovold/linux/wiki/X13s) for the current feature
+support status.
+
+## Installation
+
+Before installing, [update the UEFI
+firmware](https://support.lenovo.com/ca/en/downloads/ds556845-bios-update-utility-bootable-cd-for-windows-11-thinkpad-x13s-gen-1-type-21bx-21by)
+from Windows, then disable "Secure Boot" and enable "Linux Boot" in the UEFI
+firmware.
+
+Boot an aarch64 Void Linux live ISO using one of the "Void Linux for Thinkpad
+X13s" menu entries in GRUB.
+
+To install, follow the [chroot install guide](../chroot.md), using the "XBPS
+method", observing the following modifications:
+
+For the base installation, install both `base-system` and `x13s-base`. This
+package provides important configurations and installs the necessary
+dependencies.
+
+Before running `grub-install`, append the following to `/etc/default/grub`:
+
+```
+GRUB_CMDLINE_LINUX_DEFAULT="$GRUB_CMDLINE_LINUX_DEFAULT arm64.nopauth clk_ignore_unused pd_ignore_unused"
+GRUB_DEFAULT_DTB="qcom/sc8280xp-lenovo-thinkpad-x13s.dtb"
+```
+
+> Note: if using another bootloader, ensure the kernel cmdline arguments
+> `arm64.nopauth clk_ignore_unused pd_ignore_unused` are used.
+
+The `void-installer` script provided on Void live ISOs currently is not
+compatible with this device.
+
+## WWAN (LTE)
+
+To enable the WWAN modem, install `ModemManager` and unlock it:
+
+```
+# mkdir -p /etc/ModemManager/fcc-unlock.d
+# ln -s /usr/share/ModemManager/fcc-unlock.available.d/105b /etc/ModemManager/fcc-unlock.d/105b:e0c3
+```