[Tips] 多個microSD寫入

因為hackpad用太兇了, 先紀錄一下, 有空研究看看怎麼解決

*  https://www.raspberrypi.org/forums/viewtopic.php?t=26394
*  http://raspberrypi.stackexchange.com/questions/1098/how-can-i-copy-the-same-image-to-many-sds
* https://github.com/rockandscissor/osid