add readme

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@96 bbd45198-f89e-11dd-88c7-29a3b14d5316

bsp/qemu/build/readme

+./create-link
+make
+cp bsp/qemu/rtthread-qemu.elf $dest
+
+
+
+test OK ON:
+	Fedora 10
+	Fedora 11