[PATCH v8 8/9] bootimg_pcbios: add help and usage comments

[Vincent Davis Jr <vince@underview.tech>]

Adds comments underneath class declaration
defining plugin usage and potential
optional variables to set.

Signed-off-by: Vincent Davis Jr <vince@underview.tech>
---
 .../lib/wic/plugins/source/bootimg_pcbios.py  | 43 ++++++++++++++++++-
 1 file changed, 42 insertions(+), 1 deletion(-)

diff --git a/scripts/lib/wic/plugins/source/bootimg_pcbios.py b/scripts/lib/wic/plugins/source/bootimg_pcbios.py
index 1fa9d895bb..caabda6318 100644
--- a/scripts/lib/wic/plugins/source/bootimg_pcbios.py
+++ b/scripts/lib/wic/plugins/source/bootimg_pcbios.py
@@ -26,7 +26,48 @@ logger = logging.getLogger('wic')
 
 class BootimgPcbiosPlugin(SourcePlugin):
     """
-    Create MBR boot partition and install syslinux on it.
+    Creates boot partition that is legacy BIOS firmare bootable with
+    MBR/MSDOS as partition table format. Plugin will install caller
+    selected bootloader directly to resulting wic image.
+
+    Supported Bootloaders:
+        * syslinux (default)
+        * grub
+
+    ****************** Wic Plugin Depends/Vars ******************
+    WKS_FILE_DEPENDS = "grub-native grub"
+    WKS_FILE_DEPENDS = "syslinux-native syslinux"
+
+    # Optional variables
+    # GRUB_MKIMAGE_FORMAT_PC - Used to define target platform.
+    # GRUB_PREFIX_PATH       - Used to define which directory
+    #                          grub config and modules are going
+    #                          to reside in.
+    GRUB_PREFIX_PATH = '/boot/grub2'    # Default: /boot/grub
+    GRUB_MKIMAGE_FORMAT_PC = 'i386-pc'  # Default: i386-pc
+
+    WICVARS:append = "\
+        GRUB_PREFIX_PATH \
+        GRUB_MKIMAGE_FORMAT_PC \
+        "
+    ****************** Wic Plugin Depends/Vars ******************
+
+
+    **************** Example kickstart Legacy Bios Grub Boot ****************
+    part boot --label bios_boot --fstype ext4 --offset 1024 --fixed-size 78M
+        --source bootimg_pcbios --sourceparams="loader-bios=grub" --active
+
+    part roots --label rootfs --fstype ext4 --source rootfs --use-uuid
+    bootloader --ptable msdos --source bootimg_pcbios
+    **************** Example kickstart Legacy Bios Grub Boot ****************
+
+
+    *************** Example kickstart Legacy Bios Syslinux Boot ****************
+    part /boot --source bootimg_pcbios --sourceparams="loader-bios=syslinux"
+           --ondisk sda --label boot --fstype vfat --align 1024 --active
+
+    part roots --label rootfs --fstype ext4 --source rootfs --use-uuid
+    bootloader --ptable msdos --source bootimg_pcbios
     """
 
     name = 'bootimg_pcbios'
-- 
2.34.1