Refresh the First-run instructions.

- Move to pip
- Don't activate the virtualenv (IMO not necessary)
- Put less emphasis on docker.
- Remove the use of tail
- Refresh the logs (2011 and 2009 !)
- Explain a bit more what the commands are for.
About the name of the virtualenv, that's a very good question. I use all kind of naming for my virtualenvs. From ``buildbot``, ``buildbotEnv``, ``venv``, ... In that case, as that directory also contains the ``master`` and ``slave`` one, I thought that ``buildbot`` would be the best fit, as it correctly name everything that's under it. I find sandbox or ve too neutral, as it really goes about buildbot ...

About the code-blocks, that wasn't my impression, I thought that the lexer was being guessed on every block (if not specified of course). Maybe those snippets looks like python too much ?