Subtree merge vendor directory.txt

==Steps
1. Add remote
2. Fetch remote
2. checkout new branch at new remote
3. switch to master
4. read tree into new folder

==Example
  git remote add REPO_remote git@github.com:schacon/rack.git
  git fetch REPO_remote
  git co -b BRANCH REPO_remote/master
  git co master
  git read-tree --prefix=DIRECTORY/ -u BRANCH
  git ci -m 'import BRANCH subtree'

Example from 'Pro Git professional version control' by Scott Chacon and published by Apress
at http://progit.org/book/ch6-7.html