Doc contrib

initial doc towards github migration

imported from gerbaudo/SusyNtuple_take1/pull/3
using 
```
git --git-dir=../SusyNtuple_take1/.git format-patch -k -1 --stdout fe88ebc | git am -3 -k
# etc.
```
see
http://stackoverflow.com/questions/5120038/is-it-possible-to-cherry-pick-a-commit-from-another-git-repository