target/uml: update README

invoking uml is now simplier, not need to setup console & serial

SVN-Revision: 39632

target/linux/uml/README

@@ -17,7 +17,7 @@ build it all
 In your bin directory you will find a kernel and an ext4 root file system
 when it's finished.  Just run it like this:-
 
-bin/uml/openwrt-uml-vmlinux ubd0=bin/uml/openwrt-uml-ext4.img con=null ssl=null ssl0=fd:0,fd:1 con0=null,fd:2
+bin/uml/openwrt-uml-vmlinux ubd0=bin/uml/openwrt-uml-ext4.img
 
 The uml will start, and eventually the serial console of the uml will be at your
 console prompt.  If you would like it in xterms, substitute con=xterm and con0=xterm.