doc: Add basic overview and installation instructions

Signed-off-by: Michael Brown <[email protected]>

README.md

@@ -1,2 +1,48 @@
-SAN bootability package
-=======================
+# SAN bootability package
+
+## Overview
+
+Most Linux distributions now support the ability to install directly
+to an iSCSI (or FCoE, or other SAN protocol) target disk.  You can use
+the Linux distribution's own installer in conjunction with a
+bootloader such as [iPXE][ipxe] to install the operating system onto
+the iSCSI disk.  When you do this, the installer will automatically
+configure the installed operating system to be able to boot from an
+iSCSI target disk.
+
+If you originally installed the operating system to a local disk
+(rather than to an iSCSI target disk), then the installer will not set
+up the configuration required to support booting via iSCSI.  You can
+take an image of the local disk containing the installed operating
+system and copy it to an iSCSI target disk, but the operating system
+will not be able to boot successfully because it will be missing some
+required configuration.
+
+The `sanbootable` package solves this problem by providing the
+configuration required to allow a Linux operating system to boot from
+either a local disk or an iSCSI target.
+
+## Installation
+
+### Ubuntu
+
+Download and install the latest version of
+[`sanbootable.deb`][sanbootable.deb]:
+```
+curl -OL https://github.com/ipxe/sanbootable/releases/latest/download/sanbootable.deb
+sudo apt install -y ./sanbootable.deb
+```
+
+## Usage
+
+After installing the `sanbootable` package, you can freely transfer
+your disk image from a local disk to an iSCSI target disk or vice
+versa.
+
+The `sanbootable` code will detect at boot time whether the operating
+system is being booted from a local disk or from an iSCSI target, and
+will automatically adjust the system configuration as needed.
+
+
+[ipxe]: https://ipxe.org
+[sanbootable.deb]: https://github.com/ipxe/sanbootable/releases/latest/download/sanbootable.deb