Move long code pieces to separate files

Formatting fixes
separate files

Signed-off-by: Maurice Zhou <ja@apvc.uk>

docs/Getting Started/Arch Linux/1-zfs-linux.rst

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+.. highlight:: sh
+
+zfs-linux
+============
+
+.. contents:: Table of Contents
+  :local:
+
+``zfs-linux*`` packages provides prebuilt modules.
+Prebuilt modules are kernel-specific, i.e.,
+module built for 5.11.1 is incompatible
+with 5.11.2.
+For this reason, ``zfs-linux*``
+depends on a particular kernel version.
+
+Example: if linux=5.11.2 is available, but
+zfs-linux=5.11.2 is not available, you can not
+upgrade to linux=5.11.2 until zfs-linux=5.11.2
+came out.
+
+``zfs-linux*`` is recommended for users who are using stock kernels
+from Arch Linux repo and can accept kernel update delays.
+
+You can also switch between ``zfs-linux*`` and ``zfs-dkms``
+packages later.
+
+For other kernels or Arch-based distros, use zfs-dkms package.
+
+Availabile packages
+~~~~~~~~~~~~~~~~~~~
+* zfs-linux
+* zfs-linux-lts
+* zfs-linux-zen
+* zfs-linux-hardened
+
+Installation
+~~~~~~~~~~~~
+
+#. Check kernel variant::
+
+    INST_LINVAR=$(sed 's|.*linux|linux|' /proc/cmdline | sed 's|.img||g' | awk '{ print $1 }')
+
+#. Check compatible kernel version::
+
+    INST_LINVER=$(pacman -Si zfs-${INST_LINVAR} | grep 'Depends On' | sed "s|.*${INST_LINVAR}=||" | awk '{ print $1 }')
+
+#. Install kernel. Download from archive if kernel is not available::
+
+    if [ ${INST_LINVER} = \
+    $(pacman -Si ${INST_LINVAR} | grep Version | awk '{ print $3 }') ]; then
+     pacman -S --noconfirm --needed ${INST_LINVAR}
+    else
+     pacman -U --noconfirm --needed \
+     https://archive.archlinux.org/packages/l/${INST_LINVAR}/${INST_LINVAR}-${INST_LINVER}-x86_64.pkg.tar.zst
+    fi
+
+#. Install zfs-linux::
+
+    pacman -Sy zfs-${INST_LINVAR}
+
+#. Ignore kernel updates::
+
+     sed -i 's/#IgnorePkg/IgnorePkg/' /etc/pacman.conf
+     sed -i "/^IgnorePkg/ s/$/ ${INST_LINVAR} ${INST_LINVAR}-headers zfs-${INST_LINVAR} zfs-utils/" /etc/pacman.conf
+
+#. Load kernel module::
+
+    modprobe zfs
+
+Update kernel
+~~~~~~~~~~~~~
+To update kernel, run::
+
+     INST_LINVAR=$(sed 's|.*linux|linux|' /proc/cmdline | sed 's|.img||g' | awk '{ print $1 }')
+     pacman -Sy --needed --noconfirm ${INST_LINVAR} ${INST_LINVAR}-headers zfs-${INST_LINVAR} zfs-utils