Fix/install requirements

These commits fix a broken requirements.txt file (it produced the following reproduceable error):

```
(oonib)~/code/ooni-backend $ pip install -r requirements.txt   
Exception:
Traceback (most recent call last):
  File "/home/isis/.virtualenvs/oonib/local/lib/python2.7/site-packages/pip-1.3.1-py2.7.egg/pip/basecommand.py", line 139, in main
    status = self.run(options, args)
  File "/home/isis/.virtualenvs/oonib/local/lib/python2.7/site-packages/pip-1.3.1-py2.7.egg/pip/commands/install.py", line 240, in run
    for req in parse_requirements(filename, finder=finder, options=options):
  File "/home/isis/.virtualenvs/oonib/local/lib/python2.7/site-packages/pip-1.3.1-py2.7.egg/pip/req.py", line 1356, in parse_requirements
    req = InstallRequirement.from_line(line, comes_from)
  File "/home/isis/.virtualenvs/oonib/local/lib/python2.7/site-packages/pip-1.3.1-py2.7.egg/pip/req.py", line 118, in from_line
    return cls(req, comes_from, url=url)
  File "/home/isis/.virtualenvs/oonib/local/lib/python2.7/site-packages/pip-1.3.1-py2.7.egg/pip/req.py", line 43, in __init__
    req = pkg_resources.Requirement.parse(req)
  File "/home/isis/.virtualenvs/oonib/local/lib/python2.7/site-packages/setuptools-0.6c11-py2.7.egg/pkg_resources.py", line 2515, in parse
    raise ValueError("No requirements found", s)
ValueError: ('No requirements found', '')

Storing complete log in /home/isis/.pip/pip.log
```

The above error was due to ```requirements.txt``` containing the lines:
```
# Mirrored on Tor's webserver:
https://people.torproject.org/~ioerror/src/mirrors/ooniprobe/scapy-02-25-2013-tip.zip#egg=
```
The ```#egg=``` at the end should be ```#egg=scapy``` instead.

I have also updated ```README.md``` with a set of commands for getting ooni-backend installed on a system, including updating pip to a version (>=1.3.0) which includes the recent patches to force HTTPS for packages downloads and refuse installation if there is a hashsum mismatch. The commands also include installation and setup of virtualenv and virtualenvwrapper, creation of a virtualenv for ooni-backend, and lastly, the installation of ooni-backend without sudo inside the virtualenv.