add readme for how to flash the software images
add readme for how to flash the software images

stanxii/wr1004sjl,stanxii/wr1004sjl,stanxii/wr1004sjl,stanxii/wr1004sjl,stanxii/wr1004sjl,stanxii/wr1004sjl,stanxii/wr1004sjl,stanxii/wr1004sjl,stanxii/wr1004sjl