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.
Yes, because it's a bit more realistic example: most users usually create one buildslave, try it to make sure things work and then start asking questions about building in different environments etc.