Update docs/install.rst fix InstallationError

Following the online docs at install (https://booby.readthedocs.org/en/latest/install.html) I had the following error:

<pre>
$ sudo pip install -e git+git://github.com/jaimegildesagredo/booby.git
--editable=git+git://github.com/jaimegildesagredo/booby.git is not the right format; it must have #egg=Package
Storing complete log in /home/myuser/.pip/pip.log
</pre>

<pre>
$ cat /home/myuser/.pip/pip.log
------------------------------------------------------------
/usr/bin/pip run on Fri Jan  4 12:04:09 2013
--editable=git+git://github.com/jaimegildesagredo/booby.git is not the right format; it must have #egg=Package

Exception information:
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/pip/basecommand.py", line 104, in main
    status = self.run(options, args)
  File "/usr/lib/python2.7/dist-packages/pip/commands/install.py", line 217, in run
    InstallRequirement.from_editable(name, default_vcs=options.default_vcs))
  File "/usr/lib/python2.7/dist-packages/pip/req.py", line 65, in from_editable
    name, url = parse_editable(editable_req, default_vcs)
  File "/usr/lib/python2.7/dist-packages/pip/req.py", line 1333, in parse_editable
    % editable_req)
InstallationError: --editable=git+git://github.com/jaimegildesagredo/booby.git is not the right format; it must have #egg=Package
</pre>

I think that the right command to update in docs should be adding "#egg=booby" to url repository like:
<pre>
sudo pip install -e git+git://github.com/jaimegildesagredo/booby.git#egg=booby
</pre>

So, this works perfectly.