Add grub-efi to Dockerfile.dapper, efi.txt instructions and base grub.cfg

Dockerfile.dapper

@@ -20,6 +20,7 @@ RUN apt-get update && \
         gccgo \
         genisoimage \
         git \
+        grub-efi \
         isolinux \
         less \
         libblkid-dev \

efi.txt

@@ -0,0 +1,28 @@
+To install with EFI:
+
+A: install grub-efi
+
+apt install grub-efi
+
+B: Add to the installation process in scripts/package-iso
+
+1. Make directories ${CD}/boot/grub and ${CD}/EFI/BOOT
+2. Install the various grub modules from /usr/lib/grub/x86_64-efi/ to ${CD}/boot/grub/x86_64-efi/
+3. Copy scripts/grub.cfg to ${CD}/boot/grub/grub.cfg
+4. Run grub-mkimage to create the grub image: 
+
+(cd ${CD} && grub-mkimage  -O x86_64-efi -o EFI/BOOT/BOOTX64.EFI --config=boot/grub/grub.cfg --compression=auto --prefix='()/boot/grub' disk part_msdos fat iso9660 )
+
+NOTE: do *NOT* try to install the linux module directly in the grub image; it causes command-line options not to be passed and is a known bug.
+
+5. Add the following xorriso options
+
+    -eltorito-alt-boot -e EFI/BOOT/BOOTX64.EFI -no-emul-boot \
+    -isohybrid-gpt-basdat \
+
+This installation includes *no* additional icons or drivers. It is just meant to get RancherOS booted on an EFI system.
+If you want to add support for graphical installations, additional filesystems, and everything else.... you will need a lot more 
+
+
+
+

scripts/grub.cfg

@@ -0,0 +1,14 @@
+set default="0"
+set timeout=10
+
+set gfxmode=auto
+insmod efi_gop
+insmod efi_uga
+
+
+menuentry "Rancher" {
+        set gfxpayload=keep
+        linux   /boot/vmlinuz  quiet rancher.password=rancher rancher.state.autoformat=[/dev/sda,/dev/vda]
+        initrd  /boot/initrd
+}
+