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.
Let's not anthropomorphize Buildbot (and why would it be male?)..

Buildbot's activity is controlled by a configuration file.
We will use the sample configuration file unchanged::