Added a readme to the uml target for a quick start

git-svn-id: svn://svn.openwrt.org/openwrt/branches/buildroot-ng/openwrt@4202 3c298f89-4303-0410-b956-a3cf2f4a3e73

target/linux/uml-2.6/README

+Openwrt inside a user mode linux.  Why would we even want this many ask?
+
+There are potentially a lot of reasons, one obvious one to me, it allows
+folks to 'kick the tires' without actually flashing up any hardware.  It's
+also a great environment for porting over packages, you can get a package
+fully functional in the uclibc root environment inside a uml without actually
+disturbing your 'real router', and then rebuild for a specific target once
+it's fully tested.
+
+This is a first stab at a build that 'just works' and there will be more
+cleanup to come.  The simple directions are:-
+
+Configure for uml target
+Configure with an ext2 root file system
+build it all
+
+In your bin directory you will find a kernel and an ext2 root file system
+when it's finished.  Just run it like this:-
+
+bin/openwrt-uml-2.6-vmlinux ubd0=bin/openwrt-uml-2.6-ext2.img
+
+The uml will start, and bring up an xterm with the serial console in it.  No
+networking is configured, but, it's a starting point.  The resulting file system
+has just enough free space to start kicking the tires and playing in the world of
+'embedded routers' along with all the resource restrictions that come with that
+world.  
+
+To configure networking and more, refer to the user mode linux documentation online
+
+http://user-mode-linux.sourceforge.net/