Raspbian instructions

I forked from @Yoeori branch and just updated a few things
- remove two packages that are not available on Raspbian
- I didn't have to tweak any Makefile. I got some warning like `/tmp/cc4TQG3W.s:5332: Warning: swp{b} use is deprecated for this architecture` but I just ignored them ^_^
- Add instructions on how to create a swap/partition.

@AtnNn -- Could you review this?
I ran a few queries, and everything seemed to work (including `r.js`)

Also the build is on http://justonepixel.com/rethinkdb/raspbian/rethinkdb
Do you want to push it on our download server? Or actually, is there a rule in the Makefile to create a "clean" package?