SPI elinux wiki article

Hey all,

I've posted the beginnings of an article[1] summing up the process of bringing
up SPI on Beagle. If anyone has any contributions, feel free to edit to your
heart's content. Hopefully it will help someone avoid the agony that I went
through.

Cheers,

- Ben

[1] http://elinux.org/BeagleBoard/SPI