Added information on care and feeding of mesh extenders.

This one is more of an FYI than a serious pull request. 

I added a page of documentation on how to use the mesh extender. If I ever get the time to convert from partitions to loopback files, this is where it will explain how to recover from a crashed device. Given 2 mesh extenders, you should be able get back to one working one. Today it is just a collection of Todos. 

I also wanted a page of everything I might want to know in the field. Rather than picking out the best files on the MR3020, I just mirrored openwrt, including the attribution.