add a generic linux setup guide

docs/generic-linux-setup.md

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+# Setup Sprout to boot Linux
+
+## Prerequisites
+
+- EFI System Partition mounted on a known path
+- Linux kernel installed with an optional initramfs
+- Linux kernel must support the EFI stub (most distro kernels)
+
+## Step 1: Base Installation
+
+First, identify the path to your EFI System Partition. On most systems, this is `/boot/efi`.
+
+Download the latest sprout.efi release from the [GitHub releases page](https://github.com/edera-dev/sprout/releases).
+For x86_64 systems, download the `sprout-x86_64.efi` file, and for ARM systems, download the `sprout-aarch64.efi` file.
+Copy the downloaded `sprout.efi` file to `/EFI/BOOT/sprout.efi` on your EFI System Partition.
+
+## Step 2: Copy kernel and optional initramfs
+
+Copy the Linux kernel to `/vmlinuz-sprout` on your EFI System Partition.
+If needed, copy the initramfs to `/initramfs-sprout` on your EFI System Partition.
+
+## Step 3: Configure Sprout
+
+Write the following file to `/sprout.toml` on your EFI System Partition,
+paying attention to place the correct values:
+
+```toml
+# sprout configuration: version 1
+version = 1
+
+# add a boot entry for booting linux
+# which will run the boot-linux action.
+[entries.boot-linux]
+title = "Boot Linux"
+actions = ["boot-linux"]
+
+# use the chainload action to boot linux via the efi stub.
+# the options below are passed to the efi stub as the
+# kernel command line. the initrd is loaded using the efi stub
+# initrd loader mechanism.
+[actions.boot-linux]
+chainload.path = "\\vmlinuz-sprout"
+chainload.options = ["root=/dev/sda1", "my-kernel-option"]
+chainload.linux-initrd = "\\initramfs-sprout"
+```
+
+You can specify any kernel command line options you want on the chainload options line.
+They will be concatenated by a space and passed to the kernel.
+
+## Step 4: Configure EFI firmware to boot Sprout
+
+Since Sprout is still experimental, the following commands will add a boot entry to your EFI firmware for sprout but
+intentionally do not set it as the default boot entry.
+
+To add the entry, please find the partition device of your EFI System Partition and run the following:
+
+```bash
+$ sudo efibootmgr -d /dev/esp_partition_here -C -L 'Sprout' -l '\EFI\BOOT\sprout.efi'
+```
+
+This will add a new entry to your EFI boot menu called `Sprout` that will boot Sprout with your configuration.
+Now if you boot into your UEFI firmware, you should see Sprout as an option to boot.