CSAW CTF 2014: add ‘why not sftp?’ write-up

Closes #121.
CSAW CTF 2014: link to ‘psifer school’ exploit

Closes #120.
Merge branch 'master' of github.com:ctfs/write-ups

* 'master' of github.com:ctfs/write-ups:
  CSAW CTF 2014: add ‘why not sftp?’ write-up