Updating readme to add missing dependencies

[skrzepto]

On a fresh install there is missing dependencies. Also added additional information after appending info to shells rc file

Collecting cffi>=1.4.1 (from cryptography->fas==3.0.0)
  Downloading cffi-1.6.0.tar.gz (397kB)
    100% |████████████████████████████████| 399kB 1.2MB/s 
    Complete output from command python setup.py egg_info:
    gcc: error: /usr/lib/rpm/redhat/redhat-hardened-cc1: No such file or directory
    gcc: error: /usr/lib/rpm/redhat/redhat-hardened-cc1: No such file or directory

and

  Failed building wheel for pillow
...
...
...
        ' using --disable-%s, aborting' % (f, f))
    ValueError: jpeg is required unless explicitly disabled using --disable-jpeg, aborting

    ----------------------------------------
Command "/home/skrzepto/.virtualenvs/fas-python2.7/bin/python2.7 -u -c "import setuptools, tokenize;__file__='/tmp/pip-build-32SxGC/pillow/setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /tmp/pip-4PRI7m-record/install-record.txt --single-version-externally-managed --compile --install-headers /home/skrzepto/.virtualenvs/fas-python2.7/include/site/python2.7/pillow" failed with error code 1 in /tmp/pip-build-32SxGC/pillow/

[pypingou]

LGTM :)

[sayanchowdhury]

:+1:

[pypingou]

Let's merge then :)